A Black Hole Hostel is one that once you check-in to, you find it difficult to impossible to escape, rather like a Black Hole.  The most important ingredient is the people, the others staying at the hostel.  Other factors also come into play:  price, location, and the staff.  Below is a list of the Black Hole hostels that I've encountered in my travels.
HI Marbella This was my first Black Hole Hostel.  I checked in after returning from Morocco to rest for a day or two before getting back to my travels in Spain.  My friend, Andy, had told me that I must visit Marbella (I suspect that he liked it so much as everyone spoke English there), so Marbella I went.  What followed was a series of endless days lounging by the pool, and the frequent use of "Manana" when discussing one's date of departure.  One day, I actually packed, checked out, and walked halfway to the bus station before returning and checking back in.
Clown and Bard I think that this still ranks as my all time favorite hostel.  I've stayed there in 1998, three different times in 2001, and again in 2003.  I've only left Prague once when on the date that I originally planned and that was only because I had a flight and a job to return to.  During one of my stays in 2001, my bag actually sat in the luggage storage office for three days (I thought that if I brought it to the station in the morning, I'd have a better chance of leaving) before I eventually went back to collect it. 
Purple Pig Ah, Ios.  I stayed at this hostel/campground for 2 weeks in 2001, I meant to leave after the first week, but...I got sucked right in.  Lazy days by the pool, playing chess and backgammon, nights out on the town.  Even Graham, possibly the worst Ozzie that I've ever met couldn't detract from the Pig.
Traveller's It's the little bar at the end of street on New Town Beach in Nadi, Fiji.  The bar is among the best hostel bars that I've been to, you can charge everything to your room which is both very good and very, very bad.  You can leave to see some other parts of Fiji but you always return to Traveller's.
Solscape Raglan is filled with great hostels, but Solscape has got something special about it.  It might be the trains, it might be the Buddha, but I stayed at Solscape longer than any other hostel in all of my travels. 
Cool Bananas The newest hostel to the list and where I currently am.  Greg has spent years working in hostels in OZ and Cool Bananas seems to be his dream of the perfect hostel.  And, it's pretty damn close.
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