Rahab means "wide." His house was on the same wall of Jericho. It was a double brick wall, with an outer wall 2 meters thick, an empty space of around 4.5m. and an interior wall of 4m. Of height, these walls had 9 m.
The city, small but very populated, had built houses on the top of the wall, above the empty space between the two walls.
It is said that it was possible for the spies to choose this strategically located place, because the authorities often saw foreigners entering that house for obvious reasons. You can read the full story in Joshua 2.