The Grotto is a big rock overhang area with a cave-like feel. My guess is that a lot of people miss it by taking the elevator up and not exploring what is below the Chimney. The view ahead is of Round Top Mountain on the left with Rumbling Bald Mountain in the background. Rumbling Bald is also part of the protected area.
Continue up the stairs past Grotto and into Subway - a low passage under some rock. From here you can continue up to Pulpit Rock, this end of the Cliff Trail, or on up to the Chimney.