Initially, the good value almost made me worry this was a scam. But I decided to have a bit of faith and sure enough this is a real place. As advertised, the room is tucked in a small building in an enclosed courtyard. It's hidden behind the Hotel Liliova, which makes it a bit confusing. That being said, the check-in process was easy and the hosts made sure we had all the information we needed.
The room itself was spotless and spacious. It even includes a mini fridge and small safe for your valuables. I can confirm that despite being in Old Town off Karlova Street, it's quiet at night. Yes, there is a slight mildew smell in the hall of the building (but I didn't notice it in the room itself). I'm not sure this can be helped ... I mean, you're in Old Town Prague. The whole point is that the buildings are old, so they might smell a tad musty.
Lastly, it's worth praising this location. That's the real draw, being a 3-4 minute walk from Old Town Square and less than 10 minutes from the Charles Bridge. I would highly recommend this tiny, hidden bed and breakfast! It's a gem!