This place and the Fortaleza Guest house down the street (didnt stay there) might be the only options for the budget traveller in San Juan, and they may be the only reasonably priced things in the whole Old San Juan area, so thank god they still exist. The balcony rooms are 35$ and are huge even for two people, one has two futons and both have a fridge, a plastic table and chairs and double doors opening onto a balcony overlooking the street. There is a bar across the street that blasts music till 3am even if there's only two people in the place, so if the sounds of street noise and latin music doesn't lull you to sleep at night you might want to opt for one of the interior rooms, which I cant comment on. The hotel seems very safe and secure.
The whole place seems to be solely staffed, 24/7, by one very nice and very old man named Enrique who walks very slowly and doesnt speak much english. I'm sure he does the best he can cleaning, and the rooms are clean, but the shared bathrooms are definitely a little grungy. Not deplorably disgusting or anything but a little gross. They're so old that they could probably never look really clean, though, no matter how much you scrubbed them.
Enrique is also the guy you check in with, and since he's usually on the second floor and the gate downstairs is always locked, it can be hard to get a hold of him. There was a buzzer, but it didnt seem to do anything when I was there, so I'd recommend bringing the phone# with you so you can call him when you get there. Once he gives you your key its all good.

I arrived at around 11:30pm on a Wednesday (after calling to let them know I'd be running late after missing my flight) and was shown one of the small rooms with a "window"- but not the famous balcony room. It was extremely muggy that night so I asked for a room with A/C, which wasn't a problem. The next night he moved me to the balcony room on the first floor -which is a pretty nice room. The breeze is wonderful, esp since the room has no a/c, just a ceiling fan. Unfortunately someone else had booked that room for the next night, so I had to move again to the last room on the left on the first floor, which had two double beds and a window, which was also fine. My last night at Castro was spent in yet another room upstairs with the large balcony. This was the best, and I suspect, the biggest room at Castro. I did not experience any problems like bedbugs, although the bathrooms could definitely use some renovations-but what do you expect for 16-35/night? They do give towels so you don't need to bring your own, and also a roll of toilet paper to take to/from the bathroom if you need to go. Also, there are some "characters "hanging around who seem to live there on a semi-permanent basis. You cannot beat the location or price though, it is pretty much smack dab in the middle of Old San Jan and you can easily walk to El Morro, museums, shops, restaurant and the bus station to take you to other places in San Juan.

It was noisy on the Thursday and Saturday nights I stayed in the balcony rooms overlooking Cafe Guarinex...do not stay in those rooms if you're a light sleeper as even ear plugs won't help and music was going pretty late into the night. Luckily I love salsa and was able to fall asleep pretty easily regardless. I was traveling solo as a female and didn't run into any problems at the guest house or the surrounding areas.

The guy who manages the day to day does not speak English AT ALL...at least bring a dictionary if you don't speak any spanish.

These reviews are pretty accurate with the exception of the exposed wires in the bathrooms...not sure what thats about. I had the room with the double balcony facing the main road, made for lovely mornings, and excellent evening views. I spend very little time in my room when I travel, this place gave me everything I needed and a huge space to soak it all in.
The fact is Old San Juan is a party town and having a bar downstairs is pretty awesome if you are travelling alone or just hanging for one night or so.
Quique is sweet, sincere, and real Puerto Rican (just like me!). Great advice and enthusiasm.

Stayed in Puerto Rico en route to the Domincan Republic on both ends of our vacation. Booked 2 different hostels-both in Old San Juan. Castro's is located just above a nightclub that is open until 4am and you feel as though you are trying to sleep inside the night club. I would only recommend this place to young partygoers that plan to stay out most of the night because a good night's sleep is impossible. The bathroom is kinda scary (exposed wires, etc). Would suggest to stay around the corner at Fortaleza Guest House instead.