The last trip was held on January 4, 1997
http://www.elfstedentocht.nl/
Watching is free. Last time the NS trains had extra trains and you could get an all day pass for Friesland. Go from city to city. Great fun.
To enter the race you must have a membership card or be a pro skater (with approval). To join, you must at least 18 years old and have a skating skill statement signed by two current members of the association and declaring that you are able to make a trip of 200 km on one day to accomplish