Only the crypt remains but it is an amazing piece of brickwork. It is underneath the Church of St Menas (41.00033,28.93202), almost directly across the road from St George of the Cypresses and in an area of Samatya with an unfeasibly high concentration of churches. In the 1990s, it was used as a workshop. The Mobil car service place (Modern Oto) used to be the point of entry. When I went there in 2014, the lovely old couple in the office at the back explained that they used to be able to let people through from there but some decades ago the entrance was blocked up. I decided to hang around the doors on the street frontage, looking suspicious and taking useless photos. Sure enough, after ten minutes, two young men turned up to ask me what I was doing. At first they denied that it had been a church. Eventually, they unlocked the doors and let me in.
The place has had a bit of a transformation. The gorgeous brick dome that looks like the tomb of Atreus is looking better than ever. The space is being used to show films at the moment. The plan is to open it as a café in 2015 but official permission is slow in coming. In the meantime, it is one of the most beautiful buildings in Istanbul.
Van Millingen didn’t know of this crypt as it was only rediscovered in the 1930s. It seems to date from the 5th or 6th century.
The ambulatorio (closed passage around the outside of the church) did open as a cafe in October 2015. Unfortunately, government regulations mean that the Byzantine sections cannot yet be opened to the public. This has given rise to the ridiculous phenomenon of this cafe inside a beautiful and significant structure being wood-panelled and draped in cloth so the brickwork cannot be seen. Pictures are provided to give the connoisseur some idea of what he or she is inside.
The barista (who makes only çay and really good Turkish coffee) said that the martyrium will be open for business in February 2016, inşallah.
It isn’t. In June 2016, the kahvehane appears to have closed.
This reference is the most comprehensive recent guide to the martyrium that I can find:
Beygo, A. (2005) Istanbul Samatya’da Karpos Papylos Martyrion’u. Yüksek Lisans Tezi, Istanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü. Available online at: https://polen.itu.edu.tr/bitstream/11527/7118/1/3687.pdf Accessed 21st June 2016