The Veiled Path
Head towards the large gate at the end of the path, paying attention to the right side. Right before the tall stairs you should see a stone door leading to a location called Enigma . Go inside and shoot the yellow sphere with a ranged weapon . A group of monsters will attack you on the other side of the passage.
Once you kill them all, use Fire ball to light the nearby torches , opening the next gate. Exit through the second hole on the left and turn right. Apart from the silver key, there will be also three coloured platforms . Step onto them in the following order: yellow, blue, yellow, red, blue, red, blue, red.
If you do it correctly, the next stone doors will open . Kill the monsters and exit through the right hole. At the end of the path you will find the gold key .