Check out information on the Messenger probe - it recently flew by Mercury and sent back a lot of great images.
There is a long scarp on Mercury (a kind of cliff) that runs about 200 km - that would make some great rock climbing.
The Caloris Basin has some interesting features - some long, flat-floored troughs radiating from a central feature might make some great off-road driving.
Getting there can be a problem, but not really much harder than getting to Mars. The problem to humans would be the heat - Mercury's daytime temperature is 700K (about 425 degrees Celsius) - hot enough to melt lead.