How to get to Caverns of Endless Song
In order for you to reach the Caverns of Endless Song you'll first need to make it to Tempest Temple. For more information on How to Get to Tempest Temple follow the link provided to be taken to that guide. Once in Tempest Temple you'll want to travel to the northern most portion of the zone.
Be careful once you make it to the area with large walls of barnacle, some of the enemies in this area see through invisibility so you'll need to be extra careful on your way through. In the northern portion of this area you'll find an underwater tunnel which you can traverse to reach Caverns of Endless Song.