Which is pretty damn amazing, seeing as local schoolkids still use it for gym class.
You can read about the Panathenaic Stadium, which hosted the 1st Olympic Games of the modern era in 1896, here – but redditor KosherNazi, who posted the photo yesterday, gives a tidy summary of its renovation history:
The Panathenaic Stadium in Athens, Greece. First built in 566 BC with wooden seating. Rebuilt in marble 237 years later in 329 BC. Enlarged 468 years later in 140 AD. Uncovered and refurbished again 1,756 years later in 1896 AD in time for the resumption of the modern Olympics.
The stadium is clearly still in use. You can see people walking around (running stairs, maybe?) in the lower left. At the center of the picture is a group of local kids, supposedly attending one of the most epic periods of gym classes on the planet.
When we erect structures like this, it is always with the tacit understanding that one day, no matter how significant the monument, that structure will fall. The same fate will eventually befall the Panathenaic Stadium, but it has enjoyed a longer tenure than most structures its age, and not because it's been cordoned off. It's been cared for, refurbished, but it's still in use. It gives one pause to think about which of today's structures might still be around in 2,000 years – not just standing, but still serving the purpose for which they were built.
For comparison, redditor chronopsis points to an awesome example of an "unrefurbished" Greek stadium in Aphrodisias:
Check out the rest of this reddit thread for more cool insight into these and other Greek stadiums.