The sign on the door says No Guns and there are enough military around to make sure punters have left them at home. Inside, the atmosphere evokes a cross between a circus and a religious rally, with Buddhist rituals taking place alongside shows of physical strength.
This is Siam Stadium in the Omnoi district of Bangkok, and the young men are fighters preparing for another bout of Thailand's national sport: Muay Thai. Before the day is out one boxer will be on his way to hospital unconscious, another will have his cheekbone shattered and a third will suffer a career-threatening injury to his knee.
Siam is a rough and ready venue, much smaller than Bangkok's showpiece arena Lumpini Stadium, where the sport's gladiators have slugged it out down the years. As a capacity crowd of about 1,000 punters settles into the wooden stalls, the day's first pugilists climb into the ring in brightly coloured boxing shorts, wearing bulbous groin protectors and sporting mongkols - symbolic headbands.
But today's is no ordinary event. As bookmakers take bets on mobile phones, a sense of anticipation surrounds the big fight. In the dressing room two huge men, neither Thai, prepare to compete for a super-heavyweight championship, an event rarely witnessed in Bangkok where even the most fearsome fighters are slightly built.
Marek Oravsky, 23, from the Czech Republic, is a double amateur world kickboxing champion with a record of 37 wins from 40 fights and a feared right hook. He stands 1.83 metres tall and weighs in at 105 kilograms. His opponent is Hong Kong's Alain 'The Panther' N'Galani, 28, an Ivory Coast national and four-time African national kickboxing champion. He is 1.78m and 100kg. N'Galani and his coach and manager, Pierre Ingrassia, himself a former martial-arts champion, are a sight to behold as they approach the ring draped in the Hong Kong flag.
The formalities over, the fight begins. Two minutes later it's all over: N'Galani floors his opponent with a kick to the knee to take the World Professional Muay Thai Federation super-heavyweight championship.