The UTMB is one of, if not the most well known mountain ultra in the world. Granted, that is a fairly niche category in which to find yourself at the top of the heap. However, find yourself in Chamonix or any of the villages surrounding Mont Blanc at the end of August during the UTMB festival of running, and you might think that you had stumbled upon a big city marathon nestled away in the mountain valley. The atmosphere is, quite simply, electric, with the sounds of cowbells and shouts of "Allez!" ringing out day and night. And the finishing chute in Chamonix, where runners pass hundreds of cheering supporters high fiving kids as they go, is teeming with energy no matter the weather or time of day (or night).
Race week consists of five main events; the titular UTMB (Ultra Trail de Mont Blanc - Chamonix to Chamonix, 171 Km, 10,000 m ascent), the CCC (Courmayeur to Champex-Lac to Chamonix, 101 Km, 6,100 m ascent), the TDS (Sur les Traces des Ducs de Savoie, 119 Km, 7,200 m ascent), the newer OCC (Orsiéres to Champex-Lac to Chamonix, 56 Km, 3,500 m ascent), and the team based PTL (Petitie Trotte a Léon, 290 Km, 26,500 m ascent). They are spaced out so that there is always something going on around Chamonix, with the main event of the UTMB concluding proceedings.