The video above is the The Witcher 3 Wild Hunt The Final Trial Main Quest Walkthrough and shows how to complete The Final Trial, the quest featured in The Witcher III: Wild Hunt.
The video walkthrough covers the following objectives:
Talk to Lambert about journeying to the Circle of Elements.
Find the boat.
Kill the drowners.
Kill the water hag.
Get in the boat.
Sail across the lake with Lambert.
(Optional) Check where the boy’s voice is coming from.
(Optional) Kill the foglets.
Enter the cave.
Go through the cave.
Kill Old Speartip.
Get to the Circle of Elements.
Seek shelter in the tunnel.
Get past the blockage.
(Optional) Kill the trolls.
Light the torches around the altar.
Put the phylactery on the altar.