Here's some ideas:
1. Waterproof it and turn it into a fountain.
2. Flock the inside with aluminum foil, cut a hole in your roof, and use it as a light tube for an interior room.
3. Would make one heck of a mortar for fireworks.
4. A giant mailing tube.
5. A coffin for an astronomer? Nah, need more aperture and focal length.
6. The world's largest kalidoscope?
1. Waterproof it and turn it into a fountain.
2. Flock the inside with aluminum foil, cut a hole in your roof, and use it as a light tube for an interior room.
3. Would make one heck of a mortar for fireworks.
4. A giant mailing tube.
5. A coffin for an astronomer? Nah, need more aperture and focal length.
6. The world's largest kalidoscope?