Mostly card keys are used at large hotels in Europe but hotels in Japan still use metal keys for their guest rooms. If it is card key, the room number is not wriiten on the card and you can take it when you go outside and return it when you check out.
On the other hand, you have to leave your metal key at the reception when you go outside and ask the key when you come back to the hotel.
Therefore do not drink too much and come back late when you stay at the hotel with metal key!