i rent a safe box at my bank. depending on size you can get something for 500p for 3 months or so, 2000p for a year. not all banks have boxes available however, high demand to stash dollars lately. if you do the hostel safe box option give it a good scrutinizing, as hostels are generally not remotely safe... retiro for a locker is a good short term solution, and you can go any time of day or night, unlike the bank which is 08.00 - 13.00 only, and you need to have an account already open.