Actually in the Mario Power Tennis DK stage you can see a Minecart track (and monkeys riding one) coming out of a cave around the stage and back into the mines.
http://www.youtube.com/watch?v=ABkBMD309t4
Also in DK64 the Minecart stage for Fungi Forest leaves the mines for a section into a nice area above the trees and over a rainbow.
http://www.youtube.com/watch?v=kIzFf77Bn7c Starts at about 4:20
Thirdly there was a stage in DK Barrel Blast that is part outside and inside a mine. The tracks can be followed outside the mine as well.
http://www.youtube.com/watch?v=Yji3__ux9bU
Also (even though its not DK) Wario's Gold Mine in MKWii has the tracks extend outside the mines.
http://www.youtube.com/watch?v=ABkBMD309t4
Also in DK64 the Minecart stage for Fungi Forest leaves the mines for a section into a nice area above the trees and over a rainbow.
http://www.youtube.com/watch?v=kIzFf77Bn7c Starts at about 4:20
Thirdly there was a stage in DK Barrel Blast that is part outside and inside a mine. The tracks can be followed outside the mine as well.
http://www.youtube.com/watch?v=Yji3__ux9bU
Also (even though its not DK) Wario's Gold Mine in MKWii has the tracks extend outside the mines.