The wallet you found has someone’s whole week inside. Return it before you even open it.

Someone’s lost wallet is not really a wallet. It is their bus fare, their shift money, the card they are about to cancel in a panic, and the photo they cannot replace. Opening it starts a negotiation with yourself that does not need to happen, because the decision is already obvious before you look. Curiosity is the part that does the damage here.

Hand it to whoever runs the building, or look for a name and get it back directly. Do it before you have time to think of yourself as generous for it.