Hi Fixxxera, if it's a city that you really have to visit, then YES, I would go. Why? Sometimes, even if their system says that they are booked, if you actually go there and wait, they can at times give you a place to stay, one time I had to spend one night in the common TV room, and then they gave me a regular a room for the next evening. Also, they will often refer you to another hostel that they are friendly with. Also, in addition to hostels, depending on the city, there are private pensiones (sometimes there are representatives at the train/bus stations advertising, tourist booking offices at the stations...), etc. If you're not travelling alone, then you can split a higher priced hotel room with your friend/s. But of course, the name of the game in high season, is to make the reservation in advance, even if just a day.