Located west of Pywiack Dome. Locate cliff (note the distinctive arch). Approach can be made by hiking toward the base of Pywiack Dome (as for Dike Route, Zee Tree, etc) then making a bee line for Pennyroyal Arches or by parking a bit further down the road, directly across from the formation, figuring out which is the route du jour, then head up through the hopefully not too marshy meadow (late season better for this approach perhaps, or, a dry summer) then pick right or left of the arch. Open trees, some brush, but, fairly easy approach off trail.
The Classics
Mountain Project's determination of some of the classic, most popular, highest rated routes for Pennyroyal Arches:
The approach takes about 45 min. Longer than it looks from the road. Stay in the big trees directly below the exfoliation flake arches; stay away from the scrub trees on either side.