You've likely seen these in your FLGS and personally I used to just ignore them - I already have a grid to work on. Then I got a chance to open one of these and realized how much I had been missing out. These packs are full of illustrated puzzle pieces in the shapes of curved hallways, staircases, cavernous dining halls, and more. This means you're not drawing a dungeon onto a grid, but actually constructing the dungeon out of these shaped tiles.
They come in three varieties: Dungeon, Wilderness, and City. You can mix and match all these options to create thousands of unique maps that span multiple environment types. Imagine being a dungeon master with little time to plan and writer's block. You toss the setting appropriate tiles into a bag and then pull them at random to create your layout and reignite your inspiration for the session. Of, of course, you lay them all out on the floor and carefully construct a lethal temple to challenge the adventuring party. The options are truly endless. I seriously need to get my hands on every one of these.