Is there anything near the rune in the water at Lady Boyle's Last Party?
Normally, when there's a collectible in a particular location, it's because the designers want you to visit that location. For example, Outsider Shrines generally have runes near them.
There is a rune in the river outside Lady Boyle's Last Party. I thought that there might be a sewer entrance to the party or something that the rune was trying to guide me towards, but I looked and didn't see anything.
Did I miss anything, or is there really nothing there besides the rune in the water?
Are you talking about this one:
(Image from the Dishonored Maps App for iOS.)
If so, doesn't look like there's anything of note there. I don't recall finding anything interesting.