Travel guides mostly do not mention these underground wonders, creepy tunnels and massive underground systems. Some of these tunnels are only recently opened to public. Some are still impossible to enter and very hard to explore. But this is where the “spirit of adventure” comes in, as multitudes of amateur photographers descend into the unknown to bring back evidence of things unseen. Abandoned Salte Mine in Romania Turda Salt mine is an old closed salt mine in Cluj Country Romania.

The closed mine has long tunnels, and a deep natural cave. The excavations dug a huge artificial cave, in which you could fit three 10-story blocks. Marius says: “you can play football inside of them; and you enter there by bus”. G-CANS: Tokyo Storm Water System Here is something truly enormous, worthy of Japanese crazed super-scale imagination – vast caverns and otherworldly columns (looking like some kind of a temple) under Tokyo – an infrastructure “built for preventing overflow of the city’s major waterways and rivers during rain and typhoon season”.

Brainchild of Japan Institute of Wastewater Engineering Technology (JIWET), this “sci-fi”-like installation consists of “five 32m diameter, 65m deep concrete containment silos, connected by 64 kilometers of tunnels 50 meters deep underground. The system is powered by 14000 horsepower turbines which can pump 200 tons of water a second into a nearby river.” Tweet