Quick answer
A hotel room is a но́мер — the same word as “number”. Check-in needs your па́спорт, always.
The room
Booking
Problems
Checking in
Registration
Hotels register foreign guests with the authorities automatically — that is why they keep your passport for a few minutes. If you stay privately, the registration is the host’s job, and it matters.
Typical mistakes
Я хочу́ ко́мнату.
Я хочу́ но́мер.
A hotel room is a но́мер; ко́мната is a room in a flat.
на оди́н ночь
на одну́ ночь
ночь is feminine, so одну́.
Check yourself
What is a hotel room called?