Gord

Create a custom scenario

General Setting - Player Choice - Would highly recommend starting group of 7 just to speed up gathering resources.
Biome and enemy settings - Player Choice
Initial Resources - Plenty of Everything!

Choose Any Character you want to start with and then load into the game.

Once you load in, build your palisade, lumber mill and thatchery and assign all your people to start gathering.
If you had 7 people to start, you should have 1 person left over. Select either a foragers hut or a fishing shack to start building and assign your last person to gather some food. (People like to eat food!)

At the top bar where your resources are, keep an eye on your wood and thatch. You will need a total of 450 wood and 225 thatch to build all 3 balia's.

Once you have all the resources, open up your build menu-> Advanced Structures and start to build the balia's. Once all 3 have been built, assign 2 people to each balia and once the last person enters the bath, you'll get the achievement!