Azurite Mine - how to proceed?

Hi,
Im currently at depth : 178 . To this point I've found :
- 1 Vaal Outpost
- 1 Abyssal City so small there were no nodes in it

So i have some questions about Azure Mines mechanics (i know the tricks to find fossils and resonators) :
- The "universal one" aka : What I am doing wrong? I can't find any interesting rooms.

More detailed:
- Niko stops digging Mineshaft after A10 Kitava?
- If yes - is there any other way to face the "Mines" biome?
- Better to rush certain Depth or go Wide?
- Where are Delve Bosses?
- Where are : Runed Cavern and Whispering Gallery (for challenge)?

Thanks in advance for answers.

Yes, Niko will only dig until you get to maps.

Whispering Gallery and other nodes needed for challenge are randomly found, just gotta dig more. They are always (i think) unconnected nodes that you need to break a wall to get to.

Cities can have 0 nodes in them if you are unlucky, but just keep on delving and you will find them.

The deeper you delve, the more likely you will find good stuff.

Depth 270 = monster level 83, which is where I would delve horizontally if you dont want to delve deeper anymore, because at that level is where you can find high tier bases, highest tier maps etc.

This overview might help:

http://poedb.tw/us/DelveBiomes

Whispering galley is a Breach, runed cavern a Harbringer cave (have to find it myself, still).