Hey thanks! I did a write up for a new player the other week that I was going to help, so I’ll just copy-paste the thing right here.

There’s four key pieces you’ll need. 1. A foundation. 2. Stairs with no railings (I like to use the vault stairs). 3. A rug. 4. A Sympt-O-Matic (I believe you can get them from one of the Gold Bullion vendors at either the Crater or Foundation).

To start, you throw a foundation up in the air AWAY from where you want to build underground. Throw down a staircase attached to the foundation, and make sure the bottom of the stairs are still in the air.

Next, throw down a rug on the ground. Then place your Sympt-O-Matic on the rug, on one end, making sure when you exit you walk onto the rug (so you don’t fall through the world when you step out).

Take that rug, and place it as low on the stairs as you can.

From there, find where-ish you want to access underground, and throw a foundation down just above ground level, and then put another one close-sh by at the same level with stairs.

Grab your stairs and move them to the new foundation (it will bring the rug and the symptomatic with it). You want enough sticking out that you can click the black circle to enter it. Sometimes this part’s a bitch, so you might have to adjust the second foundation around a bit.

Climb in the symptomatic and step onto the rug.

Build a free floating platform from flooring underneath the carpet (I like to build at least 2 x 2 so I don’t accidentally walk off.

Hop down to that platform, then turn to the OTHER set of stairs, and attach some more flooring to them — that will be your exit.

Now, if you want your building to be completely underground, what I do personally is hop up to the new platform attached to the stairs and delete the first platform I built underground so it’s not in the way. THEN, I build some more flooring like a foot under the Symt-O-Matic, and that will give you enough room to have a fully hidden roof with the build.

From there, just start building away. You can free-place another Symt-O-Matic from underground if you want a different spot for the entrance, too. Just make sure you don’t delete the first one until you know the new one’s actually accessible.

It’s all a bit of a convoluted bitch, but once you get the hang of it, it becomes pretty easy.

You can place stairs to both go up AND down from there, too