A landboard, or mountainboard, is like a skateboard that has been to the gym: a longer deck, bindings for your feet and four fat pneumatic wheels built for grass, dirt and gravel. You can ride slopes and tracks under gravity, or hook up a power kite and let the wind do the pulling.
It is great fun and fairly intuitive if you have any board sport in your background, though total beginners pick it up fine with a bit of coaching. Pads are your friend while you learn to carve and stop on the rough stuff.
The instructors on adventuro can get you started with the board and protective gear. Expect grass stains, big grins and a new respect for brakes.