For its 18th branch, Thai spa empire Let’s Relax targets Thonglor’s Japanese expat crowd with a high-end bathhouse.

Nestled on the fifth floor of the Grande Centre Point Hotel, Let’s Relax Onsen and Spa Thonglor is a picture of blond-wood serenity—and that's before you even leave the lobby. 

Like at Sukhumvit Soi 26’s Yunomori Onsen, the baths themselves are separated into men’s and women’s zones (though here, in the name of authenticity, ladies don't even get the option of disposable undies).  

Amid a mix of bamboo, dark stone and the sort of dim lighting where you can't tell night from day, you'll find five baths of different temperatures, all said to offer different health benefits. 

The supposed highlight features "onsen concentrate" brought over from Japan's renowned Gero hot springs (42 degrees Celsius), while you can also take a tub in the milky-textured silk bath (40 degrees), soda bath (38 degrees) or standup whirlpool bath (36 degrees), before cooling off in the cold bath (a bracing 18 degrees).

Aside from a sauna, a steamroom, a long list of spa treatments and a peaceful tatami room, there are a few added goodies to differentiate this from the other onsens in town, namely the hot stonebed room and 12-degree-Celsius cool-down zone. 

The prices are higher than Yunomori at B650 (unlimited soak time), but then the crowds are also thinner (for now, at least). Packages start at B1,100 for onsen and one-hour Thai massage up to B4,400 for the "Bangkok Spa Experience" (hot stone massage, body scrub or wrap, facial relaxation treatment).

A small snack bar offers sandwiches, cakes and refreshments. Carl Dixon