The Cave of the Seven Sleepers on the slopes of Panayır Dağı (Mt Pion, 155m) near the northern entrance to the Ephesus ruins is actually a large Romano-Byzantine necropolis although only a small part of it is actually accessible. Despite all the signs and publicity you can only gaze down on most of the site from a rough and slippery path (this may have changed since my last visit in 2012 – I certainly hope so).
According to legend seven young local Christians were walled-up in a cave here after refusing to acknowledge the cult of the Emperor Decius (r. 249-51). Amazingly, they stayed asleep for 200 years and woke up to find that Christianity had eventually triumphed. Although they were supposedly buried here – and Crusaders apparently conveyed their bones to Marseille – there’s nothing firm to support such a suggestion; indeed excavations revealed a necropolis containing hundreds of burials.
A similar story is told about a site of the same name across country near Tarsus as well as at Afşin, near Kahramanmaraş, the site of ancient Arabissus. The story appears to date back to a 6th-century Greek pilgrim account although the details vary considerably depending on the source. It also appears in the Koran.
Even if you’re not much interested in seeing the supposed tombs this has always been a great place to come for a light lunch of gözleme (Turkish crepe) in one of the local cafes. 
Transport info
There are no buses from Selçuk to the site so you will probably have to hire a taxi. If you do that you could have the driver drop you at the entrance to Ephesus afterwards.
Alternatively, you can incorporate a visit to Meryemana (House of the Virgin Mary) into the trip.
