Line 3 of the Athens Metro runs from Dimotiko Theatro to Athens Airport, via Syntagma, although most of the trains reverse at Doukissis Plakentias: the section from Dimotiko Theatro to the tunnel portal east of Doukissis Plakentias is underground, and the section from Doukissis Plakentias to Airport is shared with Athens Suburban Railway trains, implementing a form of the Karlsruhe model. Wikipedia