"Cross country / mixed terrain", in physical training terms, specifically means across open natural terrain off roads, tracks and paths.
In 4 separate decades of service, I have never seen a unit conducting a CFT/AFT trotting across fields in merry ranks unless
a. It was a public right of way, which means it is well trodden (an of road path if you like)
b. They where lost
But I expect in John G land it happened all the time