Can the Velen "Place of Power" be accessed from the expansion DLC in Witcher 3?
That door is a puzzle normally done with Keira Metz in the "Magic Lamp" side quest at the end of the main "Wandering in the Dark" quest.
I'm not sure if you can do it without Keira to read the runes. See if you can light the torches of the four statues - you have to get the order right. This will be more difficult without Keira as the runes she reads contain a riddle giving the correct order.