How to get there eklmn to the question mark? (The Witcher 3: Wild Hunt)

Guys, this topic, on the attached picture the cursor from the mouse brought on the unknown mark - how to get there? This mountainous area, mountain high (jump on the rocks does not work, because the restrictions of textures any) on top of a huge tree in the area from the Destroyed Bastion if you go there with elite Wyvern [??] place the level i.e., I XS how much she is older than me by lvlm, I'm level 14 and a few simple belohvostov. There is a pit inside like water with blood, the walls all a spray of blood and guts and some whisper, to jump back, but broken. If you go on the water side will be cast the village in her 8 pieces of elite romannikov 26 level, BUT there is a path leading up, in the end, as seen in the picture the entrance to the cave, but he closed the massive doors, need a key, maybe someone knows where a key or the like around the unknown within?