I stumbled upon this and find it fascinating. I strongly doubt I could ever do it, maybe Kelly H. will do it in a few years :)

Ultra Trail Tour du Mont Blanc

The Ultra Trail Tour du Mont-Blanc (also referred to as UTMB) is a mountain ultramarathon. It takes place once a year in the Alps, across France, Italy and Switzerland. The distance varies between 150 and 160 km, with a total elevation gain of around 8500m. The race is run in one leg. Some believe that it is the most difficult foot race in Europe.

While the best trailers complete the loop in slightly more than 20 hours, most runners take 30 to 45 hours to reach the finish line.

From 2006, a second race Courmayeur - Champex - Chamonix (half-loop) has also been organised, and a third race was added in 2009: "Sur les Traces des Ducs de Savoie".

The race is organised by an association called Les Trailers du Mont-Blanc.
600 volunteers were involved in 2005.
The North Face is the main sponsor of this event.
Runners are supposed to carry a minimum of equipment for security reasons. This includes waterproof jacket, warm clothes, food and water, whistle, survival blanket and head torch.
There are food and drink points along the route, every 10 to 15 km. On top of that, four big "life bases" provide hot meals, beds and massages: Chamonix (France), Les Chapieux (France), Courmayeur (Italy) and Champex (Switzerland).
At Courmayeur and Champex, runners can collect a bag they previously left at Chamonix.
Runners race number contain a magnetic badge that is read at around 20 check points. The route follows basically the Tour du Mont Blanc hiking path, that is usually completed in 7 to 9 days by hikers. This is a loop around Mont Blanc.

It starts from Chamonix (1035m) and goes up to the Col de Voza (1653m) to reach Les Contamines (1150m). It then climbs to the Croix du Bonhomme (2479m) before going down back to Les Chapieux (1549m), which is the first life base. The path then runs up to the Col de la Seigne (2516m) to enter Italy, follows the ridge of the Mont-Favre (2435m) before going down to Courmayeur (1190m), the second life base. It climbs again to the Refuge Bertone (1989m) and Arnuva (1769m) before reaching its highest point, the Grand Col Ferret (2537m), which also marks the border with Switzerland. The path goes down again to Praz de Fort (1151m) via La Fouly (1593m) before reaching the third life base, Champex d'en Bas (1391m). The last part includes two rather low cols: Bovine (1987m) and Les Tseppes (1932m) separated by Trient (1300m). On the descent to Vallorcine (1260m), the path enters back France, crosses Argentière (1260m) before terminating at Chamonix, its starting point.

Slight variations are applied to the route every year. In 2007, the route was 163 km long for a total elevation gain of 8900m.

PS: there is no cash prize for winning the race ;) just glory