Ultra races have always been defined as "anything over the marathon distance" which realistically is 50km and longer.
The 50km mens event is also (currently) the longest race in the Olympic Games. Two Centurions, Don Thompson and Dominic King are British Olympians.
The Continental Centurions qualifying 100 miles "WandelWeekend" hold several intermediate distances over the weekend: 50km, 50 miles and 100km.
Many countries also hold 50km national championship races where many walkers and aspiring Olympians compete.
Classic races, especially in the UK, have ceased to be held - London to Brighton (55 miles), London to Bath (100 miles) and many more. Busy roads have meant most ultra races these days now take place in a park, although the Isle of Man races- Parish Walk and the End to End still take place on then open road as do many of the French races are also on the roads.
Other distances to try...
Apart from the straight 100 miles in 24 hour races, there are a host of other distances to try, ranging from 6, 8, 12, 48 and 72 hours through to 6 and 8 day races and 1,000 miles.
Many of the multi day races are mostly running ultras, some of which have a walking category with separate results, others don't and it doesn't matter whether you run and/or walk. The 6 Jours de France held in Privas (France) does have a walking section which is actually judged throughout.
Europe holds many challenge walks hosted by Eurodax, Rotterdam Walking Club (RWV) and OLAT walking club. RWV and OLAT host the Continental Centurions races as well as shorter races 80km and social walks.
A popular walk is the 160km/100 miles Nijmegen to Rotterdam walk held every September and organised by the RWV.
Other challenge walks to look out for, are the ones organsied by the International Marching League (IML) usually 2 or 3 day walks held throughout the world.
The UK has the Long Distance Walking Association (LDWA) which puts on walks ranging from 15 miles up to 100 miles - many of these are off road.
The Netherlands is famous for the Vierdaagse - Four Days march (distances of 30km, 40km and 50km).
The event is held in July and many Dutch, Belgian, UK Centurions take part every year as well Danish and Australian Centurions over the years.
Another popular walk is the 100km Dodentocht (Death March) which is an overnight walk starting in Bornem (near Antwerp), Belgium.
Whether a "challenge" walk, a 50km race or something shorter or longer... they are all good training events (as well as good fun!) and many Centurions will be there!
see the Fixture page for a list of events.