What is the ruling on working and receiving financial compensation for it in a hotel where intoxicants and nudity are (mostly) served, knowing that the trip was undertaken without prior knowledge of the nature of the place?

Your work in engineering inspection of air conditioning pipes in a hotel is permissible in itself, and there is no direct or intended aid to something forbidden in it. This is because hotels are built for comfort and lodging, and any evil that may occur in them is not originally intended. The sin for such acts falls upon the perpetrator or those who directly or intentionally aided in them. Sheikh Abdullah bin Zaid Al Mahmoud issued a fatwa permitting the construction of hotels and the work of Muslims in them, as long as they do not sell or serve alcoholic beverages.