In 2009, Electronic Arts came out with an edition of one of the best-selling game franchises in the world: "The Sims 3." The game is a life simulator, and you control Sims, the people of the game, by directing their actions day and night. You can also build homes for the Sims and fill them with furniture and decorations. With a little preparation, you can even build a house into a hill by creating the whole thing as a basement.
Plan out the underground house to build. This will be harder to build than many other types of houses because of the terrain's effect on the house's placement. There will be no windows or doors that lead directly to the house, and the entrance will have to be just stairs going down into the ground. You may want to do something creative, like build a "tunnel" that your Sim will walk down to get to the real house in the hill. You also may want to plan out what you'll put over your house, like trees or outdoor decorations.
Enter "Build Mode" on whatever lot you want to use.
Build the hill by selecting the "Terrain Tools" and then using the tools. Use "Raise Terrain," "Lower Terrain" and "Soften Terrain." Make sure the hill is big enough to accommodate the whole basement you have planned.
Plan a good place on the hill for the house's entrance. The stairs can extend quite high when you build them, consider how long it will take your Sim to climb them every time. You might want to disguise the location of the stairs by covering them up with bushes.
Build a basement into the hill by selecting "Basements" in "Build Mode." You click and drag to identify the location of the basement. Note that it's just an open area underground now; the basement is there, but at this point nothing looks different.
Navigate to the basement by clicking the "Go Down a Floor" button in the lower left or by pressing the "Page Down" key.
Put up the walls by selecting "Walls" in "Build Mode." Construct walls around the perimeter of the basement and walls for the individual rooms.
Continue piecing together the house by putting in the decorations, furniture and everything else. You can make it look like a regular home or give it a theme, like an underground dungeon or a cave. You may want to check out the Sims exchange and see if there are objects that would work well with your theme.
Build a sidewalk to the entrance if you want -- at least make sure the terrain isn't too hard for your Sim to navigate in order to get to the entrance.