Set apart from the frenetic bustle of one of Asia's largest cities and nestled amid the manicured gardens of Bangkok's Dusit Palace, the Amphorn Sathan Residential Hall has served as the official home of Thailand's monarch for more than a century.

Its name translates to "royal seat in the sky" but the European-style residence is known as the Ambara Villa.The royal mansion is where Thailand's King Maha Vajiralongkorn was born and it's where, as Crown Prince, he accepted the formal invitation to the crown in 2016 following the death of his father, King Bhumibol Adulyadej, which was four years ago on Tuesday.

Vajiralongkorn -- who spends much of his time overseas -- returned to Thailand this week for a host of royal duties.The King's scheduled stay won't just be a run-of-the-mill royal engagement, however. In recent months, the idea of a sacrosanct monarchy and a King shielded from public scrutiny has been torn apart by a new generation of young Thais, who are openly challenging the powerful institution.

On Tuesday, scuffles broke out between anti-monarchy protesters and police at Bangkok's Democracy Monument, which has been a meeting place during months of protests. Police said 21 people were arrested.

Demonstrators had partially blocked the road near the monument and set up a barricade, which police attempted to remove. Later, Vajiralongkorn's convoy drove past protesters for the first time. Demonstrators chanted "release our friends" and held up the three finger salute from the Hunger Games movies -- a popular symbol of the protests.

Deputy Police spokesman, Police Colonel Kissana Phathanacharoen, confirmed that demonstrators had been arrested for holding a protest without permission and detained for violating the "Public Assembly Act."

Protesters plan to gather at the monument and march to the Prime Minister's office on Wednesday and camp out there. If they go ahead they could face confrontation from pro-monarchy groups who have planned counter protests.

Experts say this week could be a watershed moment for the ongoing protest movement, which is calling for a new constitution, the dissolution of parliament and resignation of Prime Minister Prayut Chan-o-cha, as well as an end of intimidation of government critics.

Many are also calling for a true constitutional monarchy under a democratic system.Protest leaders expect a large turnout Wednesday but there are questions over whether they are pushing too hard for reform of the monarchy, and whether people will come out onto the streets during a sensitive time and October downpours.

The King is in town, it was the late King's memorial day, and Wednesday marks the anniversary of the 1973 mass uprising against military dictatorship.

"I expect that the government would control this protest very hard," said Punchada Sirivunnabood, associate professor of politics at Mahidol University's Faculty of Social Sciences and Humanities.Those calling for monarchical reform are risking lengthy prison sentences.

Thai citizens are expected to revere the monarch without question and criticizing the King, Queen or heir apparent, is punishable by some of the world's strictest lese mejeste laws. But those taboos are being broken.

What began as anti-government student-led rallies in cities across the country, has since grown into a movement attracting a large cross-section of society.

An August 16 protest in Bangkok attracted an estimated 10,000 people and in mid-September thousands came out once again, with protesters laying a plaque near the Grand Palace that read, "Here, the people declare that this place belongs to the people, not the King."

"It is now or never. The root cause of political problems stemmed from this institution, we couldn't just dance around and ignore it anymore more," said Panusaya Sithijirawattanakul, a 21-year-old student who has become a central figure of the new student movement. "Otherwise we are going to end up in the same vicious political cycle again. Coups after coups with endorsement from the King."

A direct challenge

It was a hot August night when Panusaya, who is known by the nickname Rung, first got up on stage and delivered a 10-point list of demands for reform to the monarchy.

The demands included the King being answerable to the constitution, revoking the laws against defaming the monarchy, a new constitution, abolishing royal offices, ousting the military-led government and disbanding the King's royal guards.

"I almost collapsed many times while reading the statement. I couldn't feel my feet and my hands," she told CNN. "I was afraid about the reaction of the crowd on that night."But the crowds did not leave. Panusaya had struck a nerve.

Though absolute monarchy rule ended in 1932, Thailand's King still wields considerable political influence. The image of former King Bhumibol was carefully cultivated to present him as a stable father figure who ruled by Buddhist principles throughout decades of political turbulence, and who worked to improve the lives of ordinary Thais with great moral authority.

Thailand is also no stranger to political upheaval and bloody protests. There have been 13 successful military coups since 1932, the most recent when current prime minister and former army chief Prayut Chan-o-cha seized power in 2014.

Bhumibol established tight relationships with these previous military rulers, giving them legitimacy in exchange for their steadfast support of the monarchy. Panusaya and her protest group the United Front of Thammasat and Demonstration (UFTD) say this way of ruling is not constitutional.

On September 19, she again stood up and read a letter listing the reforms personally addressed the King. The following day, with thousands still out, the group handed the demands to police, with the aim of them delivering it to the Privy Council, the King's advisers."I wanted him to hear what we want and our grievances.

Also I wanted people to know that they have all the right to speak out to the King. Everybody should be equal," she said.While Bhumibol was genuinely beloved by many in the country, his son, King Vajiralongkorn, who was crowned in May 2019, doesn't hold the same moral authority.

Vajiralongkorn is believed to spend much of his time overseas and has been largely absent from public life in Thailand as the country grappled with the coronavirus pandemic.

Last week, Germany's foreign minister said in parliament that Vajiralongkorn should not be conducting politics from the European country.While Thailand has had success in containing its coronavirus outbreak, the economic impacts have been severe.

Protesters, who say the flailing economy offers them little job prospects, have begun to scrutinize the King's immense wealth and power.

Vajiralongkorn has consolidated his power by expanding his own appointed military unit, the King's Guard. He has also vastly increased his personal wealth -- amending the Crown Property Act allowed billions of dollars worth of royal assets held by the Thai Crown to transfer directly into his control, and shares at various Thai conglomerates -- including the Siam Cement Public Company and the Siam Commercial Bank Public Company -- were put into the King's name.

The royal budget has also significantly increased."He has become the most powerful King, in terms of official power, since 1932," said Pavin Chachavalpongpun, Associate Professor at Kyoto University's Center for Southeast Asian Studies. "Even though his father had immense power, he exercised that power mostly through proxies. What makes (Vajirilongkorn) more powerful is because he exercises his power through himself."

Wider reforms

Reform of the monarchy has become an increasingly central demand but the protests are a rallying point for greater democratic freedoms, including LGBTQ and women's rights, as well as education and economic reform.

Activists say they are fed up with injustices such as the military's continued hold on power through the constitution, the prolonged coronavirus state of emergency -- which they say is being used to stifle political opposition and free speech -- and the disappearance of democracy activists living in exile.

Even high school students have joined the protests, refusing to stand for the national anthem in schools and raising the three finger salute.Mahidol University's Punchada said it's significant the younger generation are loudly pushing for change as "they don't see their future."

"We've not seen this for 40 years," she said. "They want a say in what's going on in their lives."Much of their anger has been directed at Prime Minister Prayut, whose military-drafted constitution enabled him to secure the premiership in March 2019 through a military-appointed Senate.

Young people made their mark on these first post-coup elections, voting for progressive new parties and hoping to change the old power structures that favored a few wealthy elites.

When the popular pro-democracy Future Forward Party -- which won the third highest number of votes in the election -- was ordered to disband in February, young protesters stormed the streets in flash-mob-style protests, calling the move undemocratic. Panusaya, who helped organize one such protest, said "we were outraged by the decision."

"I was like the people lost their fight again," she said.Last month, the protest group Free People led about 1,000 protesters seeking constitutional change to parliament after it voted to delay a decision on whether it will amend the constitution until November.

"The electoral system is not really democratic," said Punchada. "It's not only the students but the middle class and poor people who want to see democratic elections and a government (built) on a real democratic system."

For Panusaya, a third year student studying sociology and anthropology at Thammasat University, she's still wrapping her head around her new-found notoriety."Last year, attention barely shone on me or on our activities. And now, I have become the symbol of this movement," she said.Her family support her activism, for now, Panusaya said.

"My father is so concerned about me. My parents are supporting my decision, but they are worried about my safety."But Panusaya's protests have attracted worrying attention from authorities and she knows speaking publicly about the monarchy could be dangerous."Yes, they have put people in front of my dormitory.

I have been followed by unidentified cars or motorcycles," she said.The Thai Lawyers for Human Rights reported that 62 people have been arrested over the course of three months of protests, with some facing charges of sedition.

Panusaya said she fully acknowledges what can happen if she continues her demands but said the push for reform is too important."I know all the possibilities and troubles that could land on me, including my own life," she said. "We are aiming to spread this monarchy reform ideology as far as we can. The demands will remain at this moment."