Yado Inn is a place in Tazmily Village. It's a place where you can rest and heal yourself and party.
Spoilers: Plot and/or ending details follow.
Yado Inn is in Tazmily Village. It's owned by Jackie and Tessie. There are three rooms: one room has a Save Frog, one has nothing, and one has a resting place. In Chapter 1, Lighter rests in the second room with a broken leg. In Chapter 3, Salsa and Fassad rest in the second room. In the 3 year change, Yado Inn has become a full-fleged hotel. In EarthBound 64, Yado Inn is the same, but more western-like.
Spoilers end here.
- Ironicaly enough, the name "yado" is "inn" in Japanese.