Bouncing back post-tsunami, Thailand is on a roll, with a booming economy, a flourishing arts scene, and an efficiently cosmopolitan capital. Giddy from cleaner air and new transport, Jamie James gets a contact high from Bangkok's worldly buzz

Bangkok is one of the most heterogeneous, if not miscellaneous, cities in the world. Wandering down Sukhumvit Road, a main thoroughfare, in one block I passed a Kashmiri restaurant, a camping-gear shop, a diamond merchant, and a passel of friendly girls in red high heels in front of Pedro's Bar before arriving at my destination, the California Wow Xperience, a popular exercise club. At the entrance, speakers aimed at the street keened and thudded with techno music. Directly underneath, two old women sat on camp stools, peddling lottery tickets and Buddhist amulets, while behind them a little girl sprawled on the sidewalk doing her English homework under a banner advertising a two-for-one membership promotion.

Inside, a maelstrom of disco lights whirled across a starship Enterprise interior, with glowing video monitors bracketed in every corner. Above the reception desk, a DJ sat in a plastic cube, directing the musical energy. When I approached the desk, a row of fit young female employees executed a perfect wai in unison, touching their fingertips together and bowing their heads in the traditional Thai greeting. I told them that I had come to work out and asked for a tour; one of them, wearing a name tag that read SOM, took me on.

Room after room was packed with young Thais spinning on bicycles, running on treadmills, doing yoga, lifting weights, dancercizing, Pilatesizing. Perhaps a quarter of them were in their teens (the minimum age for members is fourteen). Som told me that more than two thousand people come here every day to work out. After we had toured the club's three floors, which are connected by glowing Lucite stairs and dedicated elevators, she brought me to a lounge with six booths; in five of them, pairs of slim young office workers and high school kids were signing contracts on clipboards.

I explained to Som that I was just visiting the city for a few days. After welcoming me, she plunged into a bit of California-style sharing. Yelping excitedly over the music, she said, "When I joined this club, it really changed my life. I started to focus on good health and positive attitude. Now I work at California Wow, which is a very positive experience for me. I am happy!" Glowing with vigor, she transfixed me with a sunny smile.

Imagine that gladsome positivity radiating throughout the whole country. On a recent ramble through Thailand, I picked up a contact endorphin high everywhere I went. There is an air of robust confidence, an ethos of cosmopolitan sophistication—a sense that the country is taking its place as the region's leader. I met a thirtyish investment banker at a cocktail party who neatly summed up the change: "We don't feel like a small country anymore." (With a population of sixty-five million, larger than that of France, why should they?)

The two of us were at the grand opening of a chic watering hole called Hu'u, on South Sathorn Road. The owner, an affable Singaporean lawyer named Terence Tan (who told me he also teaches snowboarding on Whistler Mountain, in British Columbia), could have chosen any city in Asia for this new restaurant; previously he has opened clubs in Singapore and Bali. He picked Bangkok, he said, because it's "the most dynamic, most interesting city in Southeast Asia now. It's an exciting place to be."