When walking across the Marina in Cabo you can see many touts offering to take you to Lovers/Divorce beach by boat. But can you simply walk there overland? It looks close enough, although the terrain is quite rugged.
Yes, this is indeed possible. First, walk to the Solmar Resort and ask them nicely at the gate to let you through to the Lovers beach. Then walk through the resort and go down to their beach. Turn left and head for the rock formation. Here you'll need to climb some rocks, but this should be easily doable for most people. Hike through the rocks to a small unnamed beach, then over another rock formation to reach the Divorce beach. Overall it shouldn't take more than 1 hour from downtown Cabo San Lucas.
If you want to take a boat on the way back, you can do so for $5/person - just ask one of the boats as they're dropping off passengers.