There is a bad smell in the room.
cat-TI-vo o-DO-re — both words have stress on the second syllable.
Report a bad smell at check-in or immediately when you notice it. Do not live with it for days — rooms can be sprayed or changed.
'Cattivo odore' = bad smell (literally 'bad odour'). 'C'è' = there is. You can also say 'puzza' (stench, more colloquial) or 'odore di fumo' (smell of smoke) to be more specific. Specifying the type of smell helps staff identify and fix the cause.
La camera sa di fumo.
The room smells of smoke.
Non-smoking rooms that smell of smoke are a serious breach of Italian law
C'è odore di umido.
There is a damp smell.
A musty smell suggests mould or damp — ask for a different room
La camera ha bisogno di essere ventilata.
The room needs to be aired.
A polite way to suggest the solution along with the problem
Courtyard-facing ('sul cortile') rooms in old Italian buildings can be very damp, especially in winter and in humid coastal cities like Venice. Always ask for a room with a view outward ('sul davanti' or 'sulla strada') for better air circulation.