No need to climb to the top of the tower, though there’s good loot. You’ll get to a room that has a ladder which will be your route into the tower. Once on the other side, collect the loot, then climb up some rocks in the cave. Now, if you swim around the place of power, an ‘Entrance’ marker will show up, and you’ll need to go underwater through the entrance. Jump into the water at this point and swim to the right, where there’ll be a place of power. Once you get to the tower, you’ll find that the drawbridge is up. The entrance to get into the tower is somewhat hidden. Woodland Beast (6) - Various Notice Boards in Novigrad and Northern Velen Swamp Thing (12) - Villager to the west of The Orphans of Crookback Bog ( Tip: Use Aard to knock the Foglet out of the mists so you can attack it)
Shrieker (8) - Notice Board in Crow's Perch Phantom of the Trade Route (23) - Speak with a refugee in Benek in far East Velen Patrol Gone Missing (7) - Notice Board across from quartermaster's tent at the Nilfgaardian Central Army Camp
The Mystery of the Byways Murders (22) - Notice Board in Oreton Mysterious Tracks (20) - Notice Board in Lindenvale Missing Brother (33) - Notice Board at the Inn of the Crossroads The Merry Widow (10) - Notice Board in Lindenvale When she splits into three, use your crossbow to 1-shot the parts) Jenny O' the Woods (10) - Notice Board in Midcopse ( Tip: Use Yrden to deal more damage. The Griffin from the Highlands ( Optional according to comments below, though I cannot confirm - Part of Secondary Quest: Master Armorers in Velen - Speak with Fergus, the Blacksmith in Crow's Perch, to start)