Here is a messy, but great dinosaurs tuff spot.
What you need:
- Plastic dinosaurs;
- Fish tank plastic plants;
- Rocks and pebbles;
- Water, flour and food colouring for the goo (or liquid watercolours);
- Pasta, lentils, semolina for different textures.
To make the goo just mix water, flour and colours to get a pancake batter consistency.