Sand Mountain is a popular underwater ski resort, and is also the winter equivalent of Goo Lagoon.
It is a large mountain of sand and those who go to Sand Mountain can tongue slide, ski, or snowboard just like any other ski resort.
Even though it hasn't appeared with the ski resort in the few appearances it has made, there probably is a boat parking area, as lots of locals and tourists come here.
In the episode "Pre-Hibernation Week," Sandy and SpongeBob are seen sliding. In this episode, it is revealed that guests can ski here. Two kids are also seen making a sandman (the sand equivalent of a snowman). In this episode, there is also a ramp on Sand Mountain, despite the fact that it does not appear in any other episodes that Sand Mountain is featured in.
In the episode "I Had an Accident," Patrick, Sandy, and SpongeBob are seen sliding again. SpongeBob injurs himself by breaking his gluteus maximus (butt muscle) and nearly uses the iron butt.