The Volcano Island Sims are a group of sims with an amazing landscape vaguely reminescent of Hawaii or similar subtropical volcanic islands, with many waterways, amazing waterfalls, lakes, etc. A lot of effort has been put by the Lindens who designed this part of the world to make the vegetation luxurious, the bays wonderful, and the sunsets incredibly lovely.
Mount G'al (the volcano itself) is in Mahulu near the center of the group of sims, and features LL's sense of humour. It's a "danger zone" when you fly over the volcano cone (with lava at the bottom) and you tend to drop towards the liquid lava below - a "sacrifice" to the Volcano God :)
There is a "local" mall near the Volcano Telehub - almost always very empty. I think that the original idea called for a "residential zone" with a small, local mall, specializing in hard to find items. But as usual, the building frenzy has taken over this part of SL as well, and there are empty malls, shops, and ugly buildings all over the place, like on everywhere else. A few exceptions are listed below.