Larsen's is a well-known yet hard-to-find North Shore beach. It is named after the nearby plantation owner who built a cabin on this beach, traditionally known as Ka'aka'aniu Beach. You can see why tourists call it Larsen's.
This is a fairly nice snorkeling area though it can be quite shallow, so not ideal for swimming. There are actually two beaches separated by a rock outcropping and a break in the reef with a current that will take you out to sea.
Behind the beach is a trail that leads to the furthest beach and all the way back to the trail head up the cliff. There are other trails leading down from private property, although it has a lot more rural/farm-like feel than Secret Beach with all of its mansions up the hill. I heard from one local that the trail is part of a longer, ancient Hawaiian coastal trail that should be public access but private landowners have put up barriers and a small group of people are fighting back in the courts for their rights. Land rights and private property are a big issue here on Kauai, especially as more and more rich people buy up the land, leaving the locals to feed off the crumbs from their table... not an ideal or dignifying place to be. (Go to the bottom of this page for a sermon about eating 'crumbs from the table.')