There are two parking areas for this trail, one just off the main road and one a short way up the secondary road. Both are NH State Park Parking lots and require a $5 fee. Frankenstein Cliff Trail starts on the west side of the upper lot. (These notes are starting the Frankenstein cliff trail from the upper lot) but there are trails that merge with this one that may or may not be shown on Hiking Project from the lower lot. Follow the yellow markers for this trail.
First 0.6 miles or so are mostly flat, goes parallel to Crawford Notch Rd/railroad tracks, minor up and downs, somewhat rough with fallen trees and rocks. You start much more uphill as soon as you turn southward (left) at train trestle, gets very steep once you enter the woods off the trestle area.
As you continue to gain elevation there are minor switchback to ease steepness, but the trail is generally not too well maintained and very steep. Watch your step as there can be somewhat of a steep area to one side of the trail which you can easily slide down on top of the loose material that has accumulated.
You'll get a partial viewpoint to the north at 0.8 miles in front of large rock face. After a bit over a mile, you'll get on top of the last steep area and it turns into a primarily conifer forest with a gradual incline to the first lookout. The lookout is 1.25 miles in, roughly 900ft elevation gain from the trailhead. You'll have excellent 180 degree views east of the Crawford Notch area
Continue on through the conifer forest are with slight views to left/east, moderate incline. Mostly follows close to the edge of the cliff.
At 1.45 you'll hit a fork to Falcon Cliff (0.2 miles one way), another viewpoint. You'll hit peak elevation along this trail at another very slight viewpoint (might be a bit better in winter) 1.75miles from the trailhead and you'll begin to travel downhill from there until you hit Arethusa-Ripley Falls Trail