This grotto and the spring just above it might well be where he lived and/or prayed.
Today the cave is part of the Franciscan monastery called Saint John in the Wilderness.
The service began up in the church and then continued on the steps to the grotto. This photo I took last year shows visiting Franciscan monks and priests singing the special liturgy. After the prayer, the birthday party for John began in the refectory and courtyard. It was a happy celebration!
(The church dome and the bell at sunset can be seen here in a SkyWatch post.)