First the positives:
The COOP hotel is in a fantastic location in the heart of Sofia. Everything was walkable. The breakfast buffet was nice and offered a lot of selection. We had complementary small bottles of water in our room daily. The room is spacious and well laid out. The hotel felt safe and the area around the hotel also felt safe. The hotel has a fantastic sauna and locker facilities. (Seriously - book the sauna if you stay here!)
Then the negatives:
I tried to reach out to the hotel before my stay to arrange taxi service from the train station. They never replied. Nor did they apologize for failing to reply.
The room temperature averaged 27 degrees. I called the front desk due to the discomfortable heat in the room. Twice they told me they would turn on the AC to cool the room, the third time they told me that all they have it heat and the fourth time they told me that there was nothing they could do. With my window wide open the room cooled, but then I couldn't sleep from the noise of traffic.
Speaking of sleep, the bed was terribly uncomfortable and the bedding was scratchy. Between the heat, the hard mattress and the scratchy bedding, I could not sleep well.
The room had a deep soaking tub and a shower head in the tub. There was no curtain and just a small glass wall near the shower head. The shower was powerful. So powerful that whenever we took showers we had lakes all over the bathroom floor. The small glass wall was too small and insufficient.