Behind the graffiti wall is Celica, the now globally renowned icon among Ljubljana hostels, thanks to its designation last year as the ‘World’s Hippest Hostel’ by Lonely Planet.
Rates start at €17/night in a 12-bed dorm-style room, to €24/night in one of the two-bed ‘cells’.
Celica is a former army barracks, and the ‘cells’ are/were real. (Some dizzying panoramas of the cells here.) Just a short walk from the main train and bus stations, the location is extremely convenient, but reservations WELL in advance are recommended. There are even daily guided tours.
I’ve never stayed there so can’t speak for its comforts, but the adjacent restaurant is quite good for a quick lunch.