Keystone is the small and very touristy town that is close to Mt. Rushmore. It's very convenient for going to the monument and there are quite a few things to do in this small town. The 1880 train leaves from here (and Hill City), the Big Thunder Gold Mine is here as is the Alpine Slide, and Mt. Rushmore is a short drive away. I would highly recommend staying here for at least one night for the sheer convenience of these attractions. There are tons of touristy shops that I would take care to avoid at all costs - but I'm sure others would enjoy them.