And here is the same map imported into maptool, given dynamic lighting and being explored by an adventurer who found a statue with ruby eyes and decided it would be a good idea to prise one out. The statue shudders to life, an infernal glow in those ruby eyes and the hapless adventurer wishes he'd had a bit more respect for those annals of D&D history.....
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Now obviously the labels shouldn't be visible to the players. That's why we kept them on another layer, so that by switching off the visibility of the layer (the little eye symbol beside the layer icon) we can hide them all. If we then save the map we get just the player view without any of the traps or secret doors visible:
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Now obviously this was a light hearted tutorial harking back to a more innocent time of D&D, but the basic principles you've seen here are the same basic principles that go into making far prettier maps. The core of this is getting a good selection and finding a nice way to fill it. Clearly instead of using blue for your flood fill, you could use one of Gimp's built in textures - such as the granite texture. Suddenly you have a very different type of map. Something in fact that looks a little more like this:
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But something like that is really something for another tutorial - and one by someone else as I need to get some dinner. Please feel free to ask any questions, or make comments - I will endeavour to answer them as best I can, or someone else here who is better qualified will be able to. I notice a couple of people have already chipped in with some very pertinent hints further up the thread. Thanks guys!

Oh, one final thing. Please star rate this thread with an honest rating for how useful this was. This will help other users see which threads are useful and which are not.