I might do the Zeal Ruins dungeon. Here's my idea so far:

You enter the dungeon. There's a linear path that leads to a four-way fork. If you continue going up, you'll find a room with three sealed doors. Left and right are puzzles that open these sealed doors and contain innovative tileset use. You open these and go in the middle one, but it's a trap; it shuts and you have to defeat some hard enemies to get out. At this point, you return outside to find a portal in front of the doors. It takes you deeper in the dungeon, where you begin to find the Zealians King Zeal is stocking up. Eventually, the last strentch of dungeon is a walkway over big pits (yes, this can be done with the Zeal tileset). Finally, I'll make a special room for the bomb.

Suggestions?