Beyond the waterfall is a room made of white stone. If Vincent isn't in your party, then you'll get a message stating his name when you step past the threshold of the room. So, return with Vincent. This time, there's a woman there, Lucresia, and you'll get to see a flashback of Vincent's past. While you don't get anything out of this if you visit only once, you can get Vincent's best weapon and his Level 4 Limit Break Manual if you come here with him in your party again in the second or third disc. Refer to the 'Ultimate Weapons' section for more information on this area.