Media Instructions To A Tomb?

I was exploring Gavel, and I found a mysterious entrance to a cave. As I ventured down to the bottom of the cave, there was a sign hinting to look up the waterfall also inside the cave. Following the instructions, I found more signs talking about using dynamite to enter a tomb. Does anyone have a clue on what this is about?

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Another thing, a Lusuco merchant sells Dynamite. However, on the Wiki, it says the only use for the Dynamite is a secret discovery near Lusuco. This area was located nearby the Air Temple.

 

This is an old Easter egg, that from my recent testing no longer works. There used to be a named item in a frame in the waterfall room that directed you to a button in a larger cave down the hill from the little tower with the seal cave. When the button was pressed it opened the seal for a few seconds and there was treasure inside. I think icebreaker made a video on it back when it worked

 

wish they added more little easter eggs like these
they have a chance to with 1.20 i guess

 

it still works