Right next to the Kremlin, a 17th Century monastery cracked and began to lean after builders dug a 20-meter-deep trench close to its foundations.

Geologists warn that if the city doesn't tame its appetite for digging, Moscow could collapse.

“This residential building could collapse, and they continue to sell apartments in it!” says excavator Vadim Mikhailov from Underground Research, pointing to an apartment building with cracks on the front side of it.

Vadim is an independent researcher who's monitoring geological processes under Moscow, and says nobody seems to be listening to his alarming message.

“We're now standing above an underground river. The construction nearby has disturbed its stream and the water is now washing away the soil under this building!” Vadim says.

On the surface, the Russian capital seems steady and dry, but underneath it has over 650 rivers and streams.

“Moscow is standing on a very complex geological foundation. In some places we have clay layers, and in some places we don't. That means waters penetrating the earth material either meet resistance, or they don't,” says geologist Andrey Lukashov.

Since ancient times Moscow has been expanding underground, a vast network of tunnels and corridors has been built. One such corridor collapsed in the front yard of an ordinary Moscow apartment block. Residents say it happened soon after builders started digging close to the area.

RT together with a team of professional excavators went down to explore a whole network of underground tunnels built during the time of Stalin.

“Look what water has done to the walls in this corridor: they just fall apart,” one of the diggers says, easily pulling a stone block from the wall.

Through the cramped corridors, RT made it to the Stalin era bomb shelters. The whole central part of the city has multilevel underground bunkers and cavities.

But Moscow, apparently, wants to go deeper. Officials have a plan to build a second city centre, this time underground – with roads, squares, malls, and offices.

RT asked Moscow’s chief architect Aleksandr Kuzmin if the Moscow's soil can handle it and he gave a philosophical response:

“I'm at such an age when people come to think one needs to live in the present tense, not in the future tense. Today everything seems to be ok,” he said, laughing.

While builders are digging for new parking lots and malls, geologists keep guessing where the underground waters will go, and which part of the Russian capital will crack next.