To follow up on the last post I'd like to share what happened when my players encountered my plan.
Of course, they chose the entry that I considered less likely (point A on the map, below the maintenance shaft). I knew this was possible. I decided in advance that this would be a slightly easier path, provided that they are stealthy and clever in their approach. They were slightly less than successful at the stealthy part of that contingency.
They spent much of the beginning of the session talking about letting the warforged PC sink to the bottom of the river to find where the water uptake location is. I was eventually able to explain that a trip to the bottom of the river was not necessary and that the river actually seems to dry up. Humorously, they chose to never pursue that after all. They decided correctly that it would be guarded and alarmed. They asked to look at the maintenance shaft to the sewer entrance instead. I thought that they would look at it then check out the river entrance. However, they got caught in the puzzle of how to go down the maintenance shaft instead.
To my amusement, they only barely contemplated actually going down the elevator of the maintenance shaft. Instead they decided to remove the elevator and the entire housing for the elevator from the top of the shaft and to lower the rogue down on their own. This was one of those moments where as a GM, you are happy for the players to have avoided a trap and also sad that they didn't even see it. I appeased my creative ego by allowing some engineers with the siege army (pleased to have something to do) remove the casing for the PCs over night using silenced tools. In the morning the engineers showed the PCs the trap I had created on the elevator. The trap was a cleverly covered break in the chain that would lower the PCs down the shaft for 10 feet and then drop them for 7d6 damage. It wasn't only my creative ego that caused this disclosure because the trap was also there to notify the PCs that the entrance was guarded after all. This countered previous intelligence they had received and alerted them that they would be expected.
The party cast invisibility on the rogue and had the warforged lower her down the elevator shaft. She did a great job searching and found a safe path but then she kept searching the shaft. . . including along the back wall of the elevator shaft. . . where I had a defending wizard cast explosive runes. This took the 7th level rogue to 13 hit points. With the trap triggered, the defenders swarmed into the bottom of the shaft. A rogue and a ranger started firing arrows randomly into the shaft at first missing her every time, then hearing her climbing efforts helped them figure out which 1/4 of the shaft she was in, they still faced the 50% miss chance because she was invisible. The wizard then cast Contagious Fog (Spell Compendium p. 52) at the top of the shaft. Since it descends 10ft/round there was a good chance she would fail her save at some time or another. When she failed her fort save on the first opportunity, I tried to pause long enough to allow her to use an Action Point but it didn't seem to be on her mind. She failed her save on the first round in the fog. She took 4 Dex damage, contracted the shakes, and lost her hold of the rope though her harness caught her. The players continued pulling her up and eventually worked out an escape plan for her. They cast Fly on a soldier standing nearby, got his consent, and then cast Baleful Transposition on the rogue and the soldier putting the soldier into the fog and giving him the shakes disease as well.
Once the PC rogue was out of the way, the PC wizard cast a fireball down the shaft, and singed two defenders. The PCs heard warforged footsteps running away then and decided this was still the best time to storm the entrance. They did so. The warforged tank of the PCs took a lot of damage from going first including most of the arrows from two 6th level hasted rangers and an Orb of Acid to the face from a defending wizard. The PC ranger and PC warforged killed the previously ranger and wizard (previously damaged by the PC wizard's fireball) in short order. The one remaining defender dropped his bow, walked up to the warforged PC, and with a dejected look in his eye, removed a kerchief from his head revealing another explosive rune on his forehead, this detonated right in the face of the warforged PC. The look on the players faces was a moment of GM gold. I think they were genuinely stunned. Suicide bomber warforged. Unfortunately, the explosive runes did very little damage and the warforged ranger was not killed by it. The PCs took care of that for him.
I'm still debating having their consciences catch up to them for killing a now unarmed and untrapped warforged. . . but probably won't. This campaign and this group aren't ripe for that kind of dilemma. Plus, I think their reaction to kill him ASAP was very natural.
This brought them to the acid trap/gate described in the last post (point B on the North side of the sewer system). They spent an hour or so considering it and we called it a night. We're spending some time on email between sessions trying to figure it out.
The ramification of the failed sneak attempt is unfortunate. One of the defenders hit by the wizard's fireball escaped and sent a reinforcement to the entrance. Now, the defenders know which side the PCs are coming from and the necromancer that was on the other side of the outer sewer ring (location E on the map), will move his ambush to their side (point F on the map). The Skull Watch spell will switch to the other entrance to the sewers (point F). The encounter will be very difficult. They'll face a fully prepared level 9 necromancer warforged (buffed with Augmented Summoning and a host of Summon Undead spells prepared), 2 zombie ogres, and a gray render zombie are lying in wait for the PCs, plus a 7th level changeling sorcerer will Dimension Door into the combat with 2, 8th level warforged barbarians on round 3 or 4. If they deal with the necromancer quickly, they'll do alright. Otherwise, it could be very difficult.