This cave is one of the local cavern results mapped in Coolsville that Velma's computer managed to find climate predictions for Daphne's "Saturday afternoon of cave exploring" instead of practicing for her play, "The Return of The Wife of The Son of The Vampire 2", in Daphne Has Risen from the Grave! comic tale, it is very dark and full with bats & stalactites.
Daphne invited her friends to come too, but Shaggy told her it'd be full with bats, while Scooby suggested that the cave is full with "vampire bats", but that didn't stopped Daphne who later returned to the Scooby-Doo Detective Agency clubhouse as a Vampire Daphne.
It is where Daphne hide her coffin, after "turning into" a vampire, before being exposed by the gang, who came to rescue her, to be a fraud - her dressing station and set of wires used for lavitation were found there by the afraid Scooby Doo by luck. It turned out she used this cave & "vampire story" to test her acting skills in front of a live audience.