Mass start. Long and short option.
Twists are the 'windows', where go, say S->1->2->[A,B,C,D]->7->8...
where between control 2 and 7, there's a box with 4 controls in it - you have to get them all, but the order is up to you -
Found a picture:
http://people.sju.edu/~sfillebr/Orienteering/Stumb...