Here's a 3D tessellation I've discovered with a very simple crease pattern:
I'm sure it's so simple that it can't be original. But you never know...
First you fold a grid of squares. Odd numbered sided grids work much better as oddly, they give a more even result, so 3 x 3, 5 x 5, 7 x 7, 9 x 9 etc... I find the easiest grid to prepare is the 7 x 7: just fold a grid of 8 x 8 and cut off one row and one column.
Fold all the grid creases both ways (mountains and valleys) as this will make the collapsing easier.
Then add the small diagonal creases shown in the crease pattern. You can valley these from the colour up side as only 1/4 of each set will become a mountain.
Then comes the fun part. I recommend you start from a corner and complete an outside edge first.
If you're not used to working from crease patterns, start with an easy 3 x 3 grid which will give you a model like this.
Then you can move up to five, seven, nine and so on.
Best thing is there is no set folding sequence, as with most tessellations, you just have to feel your way towards the finished model.
If you use thin paper the model can curl up at the edges, I clamp the 'locks' underneath with small paperclips for a few hours which helps. You could also dampen the model and put a weight on it but not too heavy and not too wet otherwise you'll end up with a soggy coaster!!
