The Sellaronda Bikeday is always held in the month of June. In 2015, the date is June 21. You can’t call it an event per se but it should be considered one of the greatest cycling hangouts in the Dolomites.
On this day, all the climbs that surround the Sellaronda (Gardena, Sella, Pordoi, Campolongo) are closed to all motorized vehicles from 8:30 AM to 3:30 PM. Every year, roughly 18,000 cyclists ride the Dolomite roads and – if you start early and are in a good shape – you can even ride it twice.
Here are some pictures of the 2014 Edition:
Here’s a video I made during the 2011 Edition: