The Seven Sleepers were seven Christians who had to hide in a cave around 250 AD during the Roman emperor Decius to escape persecution of Christians. There’s also another version of the story which says that they were imprisoned to death by Decius as a punishment for being Christian.
They are believed to have slept for about 180 years and awoke during the reign of Theodosius II.
Seven Sleepers is located on the northern slopes of the Mount Pion near Ephesus.
OTTI's Ephesus Tours will give you opportunity to explore Seven Sleepers.