The Olympic Games are always proceded by a furious amount of building as host cities construct arenas, pools, ski jumps, Olympic villages, and anything else the games demand. While some of the buildings are repurposed after the athletes depart, others are left to rot.

1936, Berlin

The Olympic Village
Before the WWII it was converted into a military school, but after the war it was used by Soviet forces for decades.

1924, Paris

This is the place where the legendary "Flying Finn", Paavo Nurmi won five Gold medals, including two within an hour (1500m and 5000m).

1948, London

The Wembley Palace of Engineering
This building held the fencing competition in 1948. Partially demolished in 2006, and now it's a warehouse.

1952, Helsinki

Ahvenisto Swimming Pool

1984, Sarajevo (Winter Olympics)

A Hotel on the way to Ski Jump
The Ski Jumping Ramp
The Bobsleigh Track
The Olympic Village

2004, Athens

(Photos by AP and Oceansvibe)

2008, Beijing

Beach Volleyball Stadium
Kayaking Venue
(via Limitless)
Decaying Olympic Sites As Adventure Fodder For Your Old School Science Fantasy Campaigns 

Lately I've been reading quite a few of the old 1960's and 70's post apocalyptic science fiction books. These locations just scream out for a pack of mutant apes, weird priest hoods or god knows what else to take them over. 
These places are a testament to man's competitive edge and wastefulness of money. Their perfect for a game like Mutant Future where a DM needs a pickup location. Why aren't they being used for low budget PA movies is beyond me. 
For a game like Carcosa these locations can provide another option for a time lost temple or converted buildings where tribes of coloured men have taken over. The whole area rife with "place where sports equipment artifacts can be found". 
For a space based game these places are perfect as away party locations where the players need to be very wary of the local sporting events. 
For a post apocalyptic game, a very dangerous warlord may know all of the old locations of these places and is using them to launch raids into the surrounding towns. Perhaps he's using a teleporter to take over these locations and moving into the surrounding countryside using ancient propaganda from the games.
These locations can also be used for games like Xplorers where the DM needs an alternative Earth location where the population has taken to the worship of the ancient sports gods.
These areas can be rich pickings for entire generations of artifact hunters who specialize in sporting equipment. There are also strong possibilities of generations of tribes of mutants who have turned the sports ideals into twisted military versions of themselves. The sky is really the limit when using these incredible cool locations. There are still any number of maps of these locations scattered over the web for DM's reference.

Let The games begin!