Link to map here.http://www.neotrail.org/yutc50Kcoursemap.html
The Monkey Hills are kind of between the Suspension Bridge and the boardwalk section on the east side of the park, but the north end is in the middle of nowhere on the trail.
The south end of the Monkey Trails is on the east side of the road where the north end of the boardwalk section dumps you out on the road.
Would be away easier to show, but will try and describe coming from the north.
Start on the east side of Lake Cohasset, heading south, on the trail that is next to the lake.
You will approach an intersection (Pot Smoker's Corner), if you go right it will take you to the Suspension Bridge Parking Lot.
If you go left it will wind up to the old ski hill almost heading due east, then wind back around to the south and then south west.
Stay left on trail as you wind through the brush and trees.
You will come to a T intersection that comes in from the left and goes up by some old logs and a little wooden bridge over a stone lined creek.
There is a pretty big tree down, then the trail heads across the hill on a slant and goes up.
Really tough to describe it, but very easy to find if you know where to look.