Dirty Kanza is a 204 mile, one day, "gravel grinder" race in the Flint Hills of Kansas.
"Flint" is significant because the gravel is flint, as in arrow heads, and will shred tires.
"Hills" is significant as in 10,000 plus vertical feet. While none of the climbs are long, this portion of Kansas is definitely not flat, and there are a number of short pitches in the teens for grade.
"Gravel" is significant because the roads are all gravel, ranging from smooth well graded hard pack to minimally maintained roads that are very rough.
"Grind is significant because it is definitely a grind.
Throw in a 20mph+ headwind (with no trees to block it) a few unrideable mud sections, and a river to be forded, and you've got yourself a full day.
What you don't want to do is make a wrong turn, add 21 miles, and some more vertical in the process, and finish with 225 miles, and 17 hours even.