Established in 1799, St. Mark's is today less an active church, than active East Village Cultural center. St. Marks is home to Danspace (new dance), the Poetry Project (new spoken word), and perhaps most famously Richard Foreman's Ontological-Hysteric Theater.
If you are looking for religous services, they are still offered on Sundays: 9:30am Lectio Divina (Bible study) and Sun 10:30am General Worship Service.