Pension Unitas is a former communist secret service prison. Now, it's a budget place to stay while in Prague. Vaclav Havel spent one night there, though he probably didn't want to. I stayed in Pension Unitas in August of '99. The room, located in the basement, used to be a prison cell #7 not so long ago (Havel spent the night in cell #6). The iron door with hasps and locks, and beds are all original from the prison days. Even the iron window fence is still there. The bathrooms facilities are down the hallway, and the hot water was not available in every shower stall, plus the whole place wasn't squeaky clean. The basement is appropriately called the Pink Prison--it was repainted in pink color to make it more tourist friendly. It's not a hostel and it's not a hotel. Czechs call it a "pension." The main advantage of Pension Unitas is its location--right in the center of the Old Town and a short walk to any major attraction. Also, a basic breakfast is included in the price, which is about $15 per person (I shared a triple with my friends). We figured we are still young enough, or immature, depending on one's perspective, to close our eyes on the "minor" inconveniences of this place. Besides, when does one get a chance to spend four nights in a prison cell?!
So, if you are up for a unique experience, Pension Unitas is a good choice. However, if you are on a honeymoon, you may want to look for something more romantic. :)