I have never heard of Ostrava before I saw this video. You have captured good amount of information about the coal mine in Ostrava. Honestly, Ostrava and Coal mines both are off-beat topics. However, there are two three points where i felt really concerned for you.

When you were going down 622 floors in the dark

When you went down railing below the wooden structure - my first reaction was - what if he could not come out of this pipe/wooden structure?

The changing room picture, which was captured like a horror movie scene.

I was planning to be the travel blogger, your video was an eye opener for all newbies like me who donot consider these aspects. Your video sets the real benchmark for the new comers like me. You deserved to be voted 100% by dtube account. Great going