If you discount the Olympics and the World Cycling Championships, arguably the "biggest" is the 165 mile French race -Paris Roubaix- which occurs in April. It is raced on narrow roads and over centuries-old cobbles in often times terrible spring weather conditions (rain, wind). The winner must be lucky and a strong, determined Survivor who can avoid crashes and be willing to race under the most difficult of conditions against the world's best.
In Europe, mostly in France.
Tour de France
The world's best known cycling race is probably Le Tour de France, which is held in France, which is a country in Europe.
The Baja 1000 on the california peninsula in mexico
An antonym for the word "triathlon" would be a single-sport competition, such as a marathon, swimming race, or cycling race. Triathlon involves three different sports (swimming, cycling, and running) in a single event, so an antonym would refer to a competition that focuses on just one of those sports.
Cycling
bicycle
to win the race
Tandem cycling was last held at the Olympics in 1972
Duathlon
42 minutes
Tour de france