Using the Grotto Floors you can create large hills with polystyrene foam board. You need to cut your Grotto Floor pieces to have a flat side. For quick cuts you can do at home with Meshmixer and this guide . Export the STLs and print out however many pieces you need to fit the sides of your hill.
Then cut a piece of polystyrene board or foam board that is a similar height to the grotto floor. Regular polygon shapes like triangle and squares are the best to start with. Then glue them in place with PVA – drilling and pinning with bamboo skewers helps to give them a lot of strength.
Carve the polystyrene and use polyfilla, plaster or gap filler to fill the edges between the printed grottos and the polystyrene. Once that is finished drying you can paint, drybrush and then flock.