Thieves mission help

[StardogChampion]

It's the Bravil wizard mission where I have to retrieve an arrow. There's a door in the secret cave that needs a key, but I can't find it anywhere. Where's the key?

 

[Glirk Dient]

There will be a pool nearby that goes really deep. Look on the local(not world) map and you can see there is a tunnel somewhere in that pool. It isn't very far down, so keep looking.

 

[StardogChampion]

I noticed that and went all the way to the bottom and came out into the main river, oops.

I'll look for the other tunnel now, thanks.