If you want a central hostel in Krakow, the City hostel is ideal. It's not on Rynek, but on one of the parallel streets. It's close to the central stations, so if you have to make a connection, it's ideal. The price is very good, the rooms are very clean, and it included breakfast. The only downside is that there is no elevator and the stairs are long with many stories. When I go to Krakow, I don't usually go to this hostel, but the one I normally stay in had no free beds so I stayed at this one and loved it!