Underground House Advantages

The advantages of building a house entirely underground or in a mountainside:- 

Your indoor temperature does not regulate much by the outdoor temperature. 

You are less distracted by the outdoor environment that you have less or no immediate intact with.

You can get a total darkness sleep in your room whenever you want without light or light pollution from the street. 

As much as the noise from the outside cannot reach you through transmission, the noise from the inside of your house can hardly reach the outside as well. 

You get an opened space on top of your house (roof) without a superstructure on it.

You are almost not limited to the number of stories that you want to build downwards, instead of building upwards on the ground.

The on-ground structure does not fall on you during an earthquake.

There is less or no on-ground structure exposed to vandalism.