Great question! It’s definitely possible in SketchUp. You can make organic landscapes with the Sandbox toolset (View > Tool Palettes > Sandbox), the “Eneroth Fractal Terrain Eroder” extension, the Bitmap to Mesh extension, and/or the “Artisan Organic Toolset” Extension (15 day free trial / $39). Artisan is my personal favorite method for creating terrain, but it’s possible to make terrain with all of them. You can add vegetation or animals by looking up transparent images on Google Images, then making them into 2D face-me components. You can make lakes by grouping a plane, then placing it into a valley. The “Instant Road NUI” extension allows you to make high quality pathways. Also, SketchUp is great for modeling obstacles.
I modeled this skate park with SketchUp in one day… It took me about 10 hours though. It has some terrain, obstacles, and plants.
If you want to make something more realistic, the “Skatter” extension (€99) would help… It’s amazing what they can do in SketchUp.
DISCLAIMER: Most of these things are not possible in SketchUp for schools. Although, it is possible with SketchUp Make or SketchUp Pro.