Robert Youngren posted the route:
On Margaret Island in the middle of the Danube River that flows between "Buda" on the West bank and "Pest" on the East is a rubberized track than runs 5350m around the perimeter of the 2.5km long island. (http://en.wikipedia.org/wiki/Margaret_Island).
On July 4th, 2012, while on vacation in Eastern Europe I decided to attempt to post a fast time by circumnavigating this path.
(http://www.dailymile.com/people/munisano/entries/16317729)
I (Robert Youngren) ran 18:29 (5:33 min/mile pace) for the entire 5350m loop (counter-clockwise) starting and finishing at the first light post just off the first stair case to the right off the south side of Arpad Bridge.
May not be the fastest known time (but probably was for an American on July 4th, 2012 wearing Skechers GO Bionics), but I thought I'd get the ball rolling on some other fun places to run in Europe.
Witnesses of my run were my wife Kathy Youngren and friends Luke and Brandi Hough.
---------------------------------------------------------------
There's a Strava segment for the route, which shows some faster times.
For the 24 hour version, only complete laps count, and you should report your exact finishing time for the final lap (e.g., 300 laps in 23h45m00s)
Read less 