After 20 years I stumbled across a bit of the map I never knew was there

I've been playing Baldur's Gate pretty much since it came out but last night I stumbled across an area I had never seen before. It is a corner of the map that I thought was completely inaccessible but last night my Kensai/Thief was creeping through the undergrowth and she found a rickety rope bridge I never knew existed.
This is the area that was new to me:

So do you all recognise it straight away? Am I the only person who has consistently failed to find this?
This is the area that was new to me:

So do you all recognise it straight away? Am I the only person who has consistently failed to find this?
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Comments
There are 2 phase spiders (and a web trap) in that area. If you play with SCS improved spiders though the phase spiders would almost certainly have teleported to find your party at an earlier stage in the map, so you would then find the area empty.