Sigh!!!! The rules are pretty simple. He/she who first guesses correctly can post the next picture. If they are unable or incapable of posting a picture then they should say so and its first come first served. One guess per post per person, until the guess is confirmed correct or incorrect. And if the person who guessed correctly fails to provide an image within 24 hours, they forfeit their go.
Guidelines:
Try to post a piccie where the image name doesn't give the game away. There are image-hosting websites you can use to upload your picture, if you don't have access to a website of your own. Ukcaving has a gallery, but I think it's in a coma on the long-term critical list at the moment.
Don't be ridiculously obscure - a patch of mud on the floor of an anonymous cave is plain silly, or a hole that's in a part of the country where nobody ever goes is also not really playing the game. Try to keep it within the UK.
It doesn't have to be underground. It could be cave-related landscape, or perhaps part of a club hut. Use your imagination! Keep it interesting.