Q2.50. The Sentry
Phase 1. A Tarot Card
Ask Vaska (M10.16) about the mage tower and you'll learn a new chapter in its history. She'll also give you a tarot card.
Phase 2. The Lightning Rod
Kalkstein (M8.9) tells you to find a Lightning Rod and gives you a Golem's Heart scroll.
Phase 3. Money for the Dwarf
The blacksmith (M8.7) will make a Lightning Rod for 50 orens. If you want to trade with him, you must have Zoltan's recommendation (he'll grant it to you by the end of Q2.24. Memory of a Blade).
Phase 4. The Storm
Pay the Blacksmith to get the Rod.
Phase 5. Money for the Druids
Well, now you have to get yourself a storm. Go to Druids' Grove (M10.32) and ask the elder druid if it's true that they can control the forces of nature. Pay him 500 orens to cover the expenses.
Phase 6. The Golem
After talking to the Elder Druid, go to the Golem (M10.34) and stick a Lightning Rod on its head.
Phase 7. Waking the Golem
When a lightning strikes the golem, it will wake up. Now you have to defeat it - it's quite simple, most surprisingly. You can't do much with your swords or signs - you have to use pylons. Notice that you can activate two pylons, and when you activate the third one, they all go out. The trick is to activate the third one in the exact moment when the Golem is inside the triangle - a lightning will strike it. The Golem is always heading towards you, so you won't have any problems with guiding it in the desired direction. Repeat the operation before the monster drops dead.
Phase 8-9. The Sephirah
Search Golem's body for Golem's Obsidian Heart and Neh'tza Sephirah.
Q2.51. Clay Pits
Phase 1. Drowners
When you ask Vaska (M10.16) about the problems, she'll ask you to kill the Drowners that lurk in the Clay Pits (M10.5).
Phase 2. More Drowners
Kill some Drowners...
Phase 3. Success
... and when you're done with all of them, go back to Vaska.
Phase 4. Payment
Vaska doesn't have any money to pay you - instead, you get Kezath Sephirah.
Phase 1. The Monoliths
When you get all the sephirot in Q2.29. Mysterious Tower, this quest gets activated.
Phase 2-11. Sephirah in the monolith
Run around the swamp and place the right sephirot in their spots (M8.36) (the name of a sephirah is the same as the monolith's).
When you place all the sephirot in their right locations, this quest will be over and you'll be able to enter the tower (M10.19).