good point to use some small "hard-coded" map or some extremely simple map format which can be stitched together in notepad or something like that. But Im quite positive there are lots of things Ill need an editor for when the engine and the game progresses, e.g. placing triggers, items, NPCs, logic entities and so on around the map. Also I want to use seperate meshes for the background of the tile and the platform (i.e. floor / ceiling) in that tile, which would be quite painful to do with something like notepad on the long run.
Oh, and yes, it will definitely be a tile map. Though its not 100% settled whether we need a simple 2D tile map, or perhaps we need a 3D tile map, because we might want to be able to connect 2 different halls in the Z-direction, would add something to the game... but thats not settled yet and is probably something to be added quite a time later on.
At least that simple "handcrafted" map will serve well while implementing the most basic features of the engine. 
Thx for the input!

@evolutional:
A nice idea, too, I think. So you essentially fire up the game app and enter some kind of "edit mode" where youre able to change the map the way you want it? Will have to think about that when the complexity of the game itself becomes more clear, dont know yet, whether its a feasible approach for that project, since it might well include many scripts... but an in-game editor with scripting functionality would be great :)