There is something so delicious about masturbating where you're not supposed to be doing it. I've stayed in many youth hostels around the world and some of my most fun experiences come from finding places private enough to pleasure yourself.
Frequently the shower is the best bet, especially if you shower late at night. With no one around you can sit on the floor of the cubicle with your knees up and allow the water to drum on your clit. There are no detachable shower heads so it's just the force of the water falling on you which helps prolong the ecstasy.
One of my favourite times was in a dormitory in Australia. There were six bunks in my room but only two of us sleeping in there this night. As I was getting undressed I knew that I would not be able to sleep without touching myself and relieving this burning and growing physical tension. The other girl in the room was already asleep or so I hoped. I lay on the bunk, on my side with my thighs clamped together which only served to heat up my pussy more.
I slowly slipped my hand between my legs and finally felt how wet I was. I was so turned on by the naughtiness of the situation and the possibility of getting caught that it was all I could do to contain my movements. I kept a slow and steady rhythm to my strokes, afraid not just of the sheets rustling but of the gentle wet suction noises that my fingers might make. Barely moving at all I started to build up towards a climax, aware all the time that there was another girl in the room. Knowing I could not quicken the pace or gasp out loud, I began to feel the stirrings of an orgasm. Then I came, the longest and most intense orgasm I had had in so long.
When I woke the next morning the other girl was gone. I will never know if she heard me or maybe was turned on enough to join in in her own quiet way. I like to think that maybe she enjoyed her morning shower more than usual.