Was runnning around and doing a bit of discovery. At the northeast Corner or Croockback Bog there is Grotto signpost with Cave next to it.

Found 2 chests inside and there are some destroyable rocks at the end of the cave near big chest. But not a single monster inside.

Is this cave quest related or ? What about those rocks. Any tip is appreciated.

Thanks in advance.

If you mean Dragonslayer's Grotto there's Witcher equipment in there and at the end is an illusory wall.
That's the only cave I can think of that's northeast-ish of Crookback Bog.

Nope that Cave is at Grotto signpost. North of Belek, Northeast of Toderas, South of Ferry Station and East of Marauders' Bridge Signposts.

If you open map with Dragonslayer's Grotto its northeast corner of that map. Really close to Pontar River.