Downstairs (adverb)

1. On or to a lower floor or level in a building.
2. Below or under the level of the ground.

Origin:

From down +‎ stairs.

Examples:

1. She went downstairs to get a glass of water.
2. The laundry room is downstairs.
3. The bedrooms are upstairs and the living room is downstairs.
4. The basement is located downstairs.
5. The restaurant has seating both upstairs and downstairs.