Well, I started building a dragon cave on January 7th when I was asked to DM a one shot D&D level 20 "Dragon Hunt" adventure... didn't have much to go on, I couldn't find anything on the web, so I started off with sketching a few ideas out.

January 7th:

After half of a day of thinking (at work) I started in on the foam. You can see part of my pen drawing / outline on the foam.

Here it is with the Colossal Red Dragon for sizing.

January 8th:

By 3:00am I have finished the basic blocking of the back half of the dragon's cave... I threw in a few dragons for sizing... I wanted this cave structure to work for other things besides just a Colossal Dragon Hunt. Gargatuan, Huge's, etc... plus maybe Lich caves and some other stuff. Dwarven caves thrown in with a few Huts. Who knows...

January 9th:

Another late night / early morning (3:30am this time) leaves me with the lower half carved in a bit more... still need some detail work up above though.

January 10th:

I forgot to take pictures of a lot of this, but I managed to finish the detail work up above, and paint the lower section and most of the upper. I also poured the lake out of Envirotex Lite.

The back half

January 11th (early morning):

Here is a picture of the progress as of 1:40am on Saturday morning. The fan is helping to cure out the envirotex lite. I added a bunch of detail paint after this...

January 11th (evening, game time):

Here is the group of PC's entering the cave... Vampire Blackguard on Red Dragon Steed, Dwarven Assassin, Pixie Arcane Trickster, Dwarven Immovable Dude, Druid who is never in human form, Human Archmage, and Gray Orc Cleric.