Please note I've "borrowed" (OK, stole) the technique from Jeremy P. and his youtube channel "Black Magic Craft". He's very creative and has a lot of useful "how-to" content on his channel.
There are a lot of commercially available dungeon tiles on the market but they can be expensive and heavy. Plus there seems to be a general convention of 2 inch x 2 inch base size which makes set up rather hard - lots of pieces. Plus, I just wanted to make something different.
Step 1: Cut out the foam pieces, in this case we're making a "U" section. My tiles are based on 4 inch x 4inch size with 1.5 inch high walls. I tested a lot of wall heights from 0.5 up to 4 and found that 1.5 had the best mix of looks and utility (players can see and easily reach their figures. It's important to cut these out as exact as possible so I use my trusty Proxxon Hot Wire table cutter. If you like to make terrain out of EPS foam then you should get one - it's the most useful hobby tool I have.
All of my walls are 0.5 inches think. Remember to take into account wall thickness when cutting pieces the abut together. The "U" section has three walls 2 that are 4 inches long and 1 that is 3 inches - since it connects with the other two walls it needs to be shorter by 2x0.5 inches!
This technique does allow one to release some aggression and I can often be heard muttering "What did that Orange Moron say now?...."
I'm also experimenting with some tiles that incorporate LED lights - you can see some tests in the upper right of the picture.
None of the tiles will have doors - I'm using slide on doors that fit over the 0.5 inch wide walls. I'll do another tutorial on doors and other details.