Really fantastic stay at Gustavo's place. I can't imagine a better location if you want to be in Old Town. It's essentially only 1 street over from Old Town so you have direct access without constant noise and madness. It also has an INCREDIBLE balcony to relax on when you're in the apartment.
Gustavo was also an incredible host. I was in San Sebastian early and he was very flexible on the check in process. He gave me several fantastic recommendations for places to go while in San Sebastian, and answered my questions during the stay in a very timely manner. Would highly recommend.