The infamous Bokor Hill Casino/Hotel in Cambodia was originally built as a retreat for French Colonialists in the 1920's who wanted to escape the heat back in Phnom Penh. It was abandoned by the French during the Indochina War and was one of the last Khmer Rouge strongholds up until the 1990's.
Situated on top of a mountain, it isn't really the most convenient place to get to. It requires a number of uncomfortable rides on a pick-up truck (with 24 of your closest friends) and a 1.5 hour jungle trek, one way. Today, there is a $1B development going up on Bokor Hill, which boggles my mind because of the questionable location. Oh yeah, all of this in the middle of a national park.
I suggest you have a look at the entire set of photos on my Facebook Gallery, as I think it is one of my best urban exploration series.