I made sure to emphasize to my players the difficulties of getting to the keep.
- To get around the Lizard Folk you'd have to move through the swamp - and lizard folk are a lot better then you knee deep in swamp water
- An attack from the rear will allow the keeps defenders to get the Lizard Folk in a crossfire
There was, of course, a map for the Lizard Folk Lair. Here I find myself making some fairly substantial changes. First off I did not want to have a series of encounters each with 5 lizard folk or something. That sounds pretty boring.
I choose to consolidate the initial encounters down to one with the Harpy's and the dangerous plants for one encounter. Then I created another that featured most of the standard lizard folk pouring into the Otyugh's lair which I put into the centre of the lair with Lizard Folk living quarters radiating out from that room.
After that I designed a series of encounters that where pretty much in a straight line. The Lizard Folk lieutenant, then the role playing encounter with the Lizard Folk Shaman, then the Lizard King, the kobolds and finally the egg chamber.
Note the map also has layout for The Terror Below for the final encounter of the adventure.
Here is the map.
Encounter At Blackwall Keep