They needed construction material when they were building Odessa. Since there are shell rock deposits in the area, which is great for construction, they extracted it chaotically, which resulted in appearance of an entangled 3000-kilometer underground tunnel.
So, we're in a drainage which connects to abandoned bomb shelters, old galleries and stone pits. This is a waggon they used when they were building the drainage.
This Odessa mini-underground was built in the 60s. It's not used though.
In some places drainage archs are just hollowed out in shell rocks.
We're 40 meters underground.