Excellent entry to Ultramarathon during the night on a more or less flat course compared to other Ultras. And the runners can be accompanied by a cyclist on a MTB. The top 10% are running the course below 10 hours.
(From Wikipedia) The Biel Running Days (D. “Bieler Lauftage F. “Courses de Bienne”) takes place in June in Biel/Bienne, Switzerland. Various long-distance track events are involved. The most well known of these is the 100km Ultra marathon which began in 1959 and is one of the biggest and oldest of its kind (only a 1x100km loop). You can do the run alone, as a couple or in a Team of 5. The Ultra marathon is also a part of the European Ultramarathon Cup. Along with the 100 km Ultra marathon there are a night marathon and a half marathon taking place.
Swiss TV review of the 2012 race: