You will need grass, stone, and wood for the construction. If you want to build an underground base, the first thing you need to do is collect some material. But, don’t worry stone tools can do the trick. If you are just starting the game, it’s going to be a little harder for you because you lack the proper tools.
The base can also be upgraded depending on your taste, for instance, if you want castles instead of simple bases, you can do it. The method I use to build an underground base is tested in the early, middle, and the late game. Or probably you have been playing the game for a while, and you are unsatisfied with your current base, or simply you just want a safe place to spend a night in without zombies tearing up your house down and bothering you while you craft your stone ax and clubs. If you are new to this game and want to find a place where you can safely put your stuff while you go out and explore, you have come to the right place.