According to the Nintendo Power Player's Guide, there's a Secret Grotto in Lon Lon Ranch (around the southeastern area), but I have no idea where exactly. I've bombed all around there and used Song of Storms, to no avail.
Plus, I'm playing the VC version and thus have no access to a Rumble Pak.
Eh, interesting idea, but that doesn't appear to be the case. I tried the tree just outside Lon Lon, and nothing happened. Plus, that tree is in a different place than where the secret grotto is indicated. That, and all Hyrule Field grottos are already marked on NP's Hyrule Field map.
i know the one youre talking about, and its further north of lon lon go to the northwest corner outside lon lon, find the "bend" in the road up there, and follow it to a lone tree, then a gap, then some forest. bomb the lone tree.
I think it would be neat to be able to swim underwater ~Mimbrate_Knight