There are two distinct parts to Pension Unitas. The site was once the site of a police prison and so downstairs, in the basement, you can stay in the former cells. The most famous inmate of the prison is Vaclav Havel, who stayed in the cell just a couple along from us.
Each cell contains a set of bunks, a washbasin, a hanging rail for clothes/towels, a bookcase and a table and chairs. There is a small window which is useful because it can get quite warm in the basement. Each corridor has a couple of showers and washrooms and there are toilets every couple of cells along.
As you would expect, these rooms are tiny, but in a city like Prague you're unlikely to spend much time in the hostel! We found that we weren't disturbed much in the early hours but did find it noisy in the morning (around 6:30am) when some people were leaving. We did have to get out of bed and ask people to be quiet.
We stayed here a second night but this time upstairs in a pension room. The room was very spacious but didn't contain much more than the cell room! There was a proper wardrobe, though, and two single beds. It was light, pleasant and airy. There were shower rooms just along the corridor and there seemed to be an adequate number because the place was pretty full and we did not have to wait at all for a shower to become free.
Breakfast was included and was not particularly inspiring. There was muesli (though I am allergic to nuts), a few different kinds of bread, cold meat, cheese and jams. There was weak orange drink, weak coffee and tea.
I would recommend either the prison rooms or the pension rooms to anyone on a budget. The location is good, close to two underground stations and well-placed for the main tourist attractions (only 5 minutes' walk from the Charles Bridge) and there are bars and restaurants nearby, without it being noisy at night.
Accommodation in the Prison part was 1,000 Czech Crowns per night (for two people) and in the pension rooms 1,4000 Czech Crowns, again for two people.