One Bridge, One Village, One Terrace
Kırkpınar, the Justinian Bridge, and Ayrı Gezegen
Kırkpınar
Kırkpınar is a lakeside neighbourhood of Sapanca, a short drive from the town, with a botanic park and the pedestrian Bağdat Street. It works as a calm first or last stop: a walk, a tea, then back to the car. Lakeside hotels here, including properties signed as Kırkpınar Sapanca, are normal pickup and drop-off points. The hotel's own breakfast, pool, or room is reserved with the hotel.
Justinian Bridge, also called Beşköprü
There is one late-Roman bridge to plan, not two. The Bridge of Justinian (Justinianus Köprüsü) is the structure also known as the Sangarius Bridge and, locally, Beşköprü. It stands in the Beşköprü neighbourhood of Serdivan, southwest of Adapazarı, on Çark Deresi, the stream that drains Sapanca Lake toward the Sakarya. The Sakarya Governorate records a limestone bridge of 365 metres, 9.85 metres wide, with 12 arches, built in 558–560 under Emperor Justinian I. It was placed on the UNESCO World Heritage tentative list in 2018. Older write-ups that list "Justinianus Bridge" and "Beşköprü" as separate photo stops are describing the same monument. It is an easy extra on the Adapazarı side, not a second lake circuit.
Ayrı Gezegen glass terrace
Ayrı Gezegen Cam Teras is in Maşukiye, at Kartepe Caddesi No. 179, Kartepe / Kocaeli — on the Kartepe road, not in Serdivan. Published hours are daytime, often opening at 09:00 and closing in the evening; the exact closing hour differs by source, so check that morning. The glass platform is a paid entrance. Adventure-park activities sold at the same site are a second purchase. From central Sapanca the approach is a short mountain-side drive; it is still the same time budget as any other Maşukiye stop, not a free extra after a full Ormanya visit.