Paper-thin walls!
Even though I traveled alone to this hotel, I felt like I shared my room. I don't appreciate having to listen to other guests' television all night, hear conversations as if they are happening in my room, or be bothered by other toilets flushing. All of those things were slightly more pleasant than the grunts and groan from the neighboring room. I would never stay in this hotel again. Travel already has the potential to be unpleasant without getting a horrible night's sleep because of all the noise in the rooms next door.
Additionally, there was a very unpleasant, sewer gas type of smell between my room and the elevator.