hmm -- does that work? It would obviously have lots of water and things growing. Which would militate the necromancy he works.
But it does have to be dark, otherwise the solar magic doesn't have the foil it needs. (This is how it would have to be a swamp, not a marsh; not enough shade.) A dark desert is hard to build, and then to describe, and would be under the effects of the sun already. (Unless it was cold? But then it would likely be white.) Caves would not work for other plot elements.
Perhaps I shall emphasize the sun's drying up of water, and the decay in the swamp.