The New World Heritage Site the Trans-Iranian Railway:

No fewer than 224 tunnels total more than 76 kilometers in length, while 174 viaducts and 186 smaller bridges carry the railway across deep ravines and river valleys as it climbs to two 2,134-meter (7,000-foot) summits.

https://edition.cnn.com/travel/article/trans-iranian-railway-cmd/index.html