d10 Table: What's Blocking the Tunnel?
1. Bloated, decaying corpse of giant purple worm with 1d8 giant rats gnawing through the corpse.
2. 1d8 dead Xvarts.
3. Melting gelatinous cube.
4. Roof collapse; support beams show signs of damage by magical fire.
5. 1d8 tons of humanoid fecal matter.
6. Large boulder held in place by several cross beams spiked into tunnel walls.
7. 1d8 x 1,000 freshly molted snake skins.
8. Tunnel not truly blocked; it's only an illusion.
9. Tourist information booth manned by 1d8 rock gnomes eager to please.
10. Toll booth with 2gp fee. Phantom toll booth operator will mercilessly hound toll skippers at inopportune moments for 1d8 days or until toll is paid.