A World of Real (Mostly) Naked Guys (blog) has a recent post showing a Warhol-like video with a the main character naked in bed and sleeping with an erection that grows then fades. There is also a link to that blog on the right hand side bar here (the blogger has also linked back to mine).
http://www.nude-guys-world.net/article-22377559.html

This brings up another form of male-male homoerotic communication (CMNM experience) that I find to be absolutely spellbinding - especially when it is happening to me: sleeping with another guy - particularly when either I or he is nude.

A naked guy sleeping in a hostel room -->

 
I happened to me recently when I was staying in a hostel during August. I had the 'hardest' time getting to sleep because there were mostly unclothed guys (wearing only boxers or boxer-briefs) in the bunk beds around me. I always sleep naked during the summer months, and when I am staying at a hostel - I usually do so, too. In most cases, the sheet keeps me covered but at times, I'm sure my cock - soft or erect - is plainly visible. I have found many guys at the hostels who sleep in the nude.

How to find a hostel
Google will help (as you must know). It helps to try Google in various languages, especially the spelling of the city is different between specific languages.

Cologne is very different in Germany and French. I found an interesting link (for Germany's hostel/backpackers) ...for example.http://www.backpacker-network.de/home/ 

This site listed only two hostels (I am sure there are more), but it also has city info (listing straight bar, gay bars, restaurants and tourist spots, along with other helpful hints).  If you don't get specific advice from anybody here, then try a more generalized travel site (esp one with travelogs or traveler's recommendations).

You should take a look at such sites as TravBuddy or Virtual Tourist, or TripAdvisor (heavily commercial), TravBuddy listing for Cologne ( a sample city with a large gay community and Pride festivities)
http://www.travbuddy.com/Cologne-travel-guide-391589

Other sites worth looking at:
http://travbuddy.com
http://www.virtualtourist.com
http://www.TripAdvisor.com

Also the major hostel listing are at:
http://www.hostels.com

http://www.hihostels.com (Hostelling International chain)
http://www.hostels.net/ (reviews of hostels)
http://www.hostelz.com/
 http://www.hostelworld.com/
http://www.hostelbookers.com/