Safe Haven is a quest in Chapter II which Geralt hears about from Zoltan. He only gets the details from Leuvaarden, the person actually in need of his services. It seems drowners are wreaking havoc on Leuvaarden's business interests at the landing in the swamp. He will pay to have it sorted, pronto.
The very first step is to speak with Zoltan Chivay about work for a witcher in Vizima. He will tell you that Leuvaarden needs help with some problems down at the dike. Once you are able to access the dike, find Leuvaarden and speak with him to get further details, then use the services of the ferryman to go to the swamp. Once there, you will find a fireplace near the large tree by the landing. Meditate there until midnight, or wander around the swamp doing other stuff until midnight-ish. Then, roam the small area between the landing, the fireplace and the woods. One-by-one drowners will appear. Keep killing them until you get a status update on the quest.
The Merchant Edit
The merchant Leuvaarden apparently has some work for a witcher. I can find the merchant on the dike, where he conducts business in daytime. If I mention our mutual friends, I will easily get the assignment. I should go to the Dike, where I can expect the merchant Leuvaarden to have a job for me.
Drowners in the Swamps Edit
Leuvaarden offered me 400 orens for killing drowners. I should use the boat to get to the swamps and get rid of the monsters that have been haunting the harbor at night. I must use a boat to get to the swamps and get rid of the monsters who come to the harbor at night.
The Reward Edit
I killed all the monsters — time to collect my reward from Leuvaarden. I will find him on the Dike. It's time to go to Leuvaarden to collect my reward. I will find him on the dike. (500 XP)