They sent me to a different hotel
When I arrived, I was told that they'd overbooked and my room was not available. They claimed that booking.com hadn't notified them in time, but I'd exchanged email with them and sent me a copy of my passport over a week before arriving. They sent me to another hotel, which was supposedly actually a better hotel (it was right by the city center), but it was further from where I was actually going. While changing hotels I missed the beginning of the conference I'd come to attend.