Puzzles for sewer adventure?

[Valtane Beastblade]

First off, anyone playing my campaign should look away now. You know who you are.

I'm running the first adventure of my campaign next week and would like the adventure to be more than just a series of combats, but I'm at a loss for how to do this within the constraints of the dungeon.

The main plot involves the PCs having to retrieve a collector's magic ring that was stolen by Magnimar's sewer goblins. The goblins have made their lair in a long-buried ruin that intersects with the sewer system. Unfortunately for trying to create a problem-solving aspect, sewers tend to have little in terms of traps or puzzles and the ruin itself can't have anything too complex for goblins to figure out, as they can't hide the ring in a chamber they don't know how to enter.

Any ideas on how to include more problem-solving here?

[MyCupRunnethOver]

Turning on water valves to float up impossible to climb slim covered causeways to access secret doors or intersecting tunnels is always fun. Or reverse, letting water out of a cistern to equalize levels with another chamber to go down or drain a water filled passage. Even goblins can grasp that and combinations make for good puzzle fodder.

A flammable substance on the top of sewage makes a good trap. The general best avoidance for which is diving into the sewage, incurring a stench you bad guys with scent can use to track the PCs, the sickened condition and/or disease.

[Ashtathlon]

stopping the air flow to cause a build up of flammable gases, that once they accumulate to the point where a prone goblin can light them for a upward explosion of gas to be ignited (gobbos love fire..explosions and risk of death)
the upward pressure will cause a secret door to open etc..
A few bungled tries can cause some pc harm...and the small size and prone being the only way to take minimum damage. (without alternate means)

a series of holes in the wall that have some form of unnatural darkness that requires the pcs to stick their arms in and fumble for a switch/dial/lever...can have alternates with beartraps..poisonous vermin..slime..etc in it.

Play name that floaty in the sewage with a crazy gobbo for a password. :)

[Valtane Beastblade]

Great ideas so far. The lair was going to have some raised walkways over a pool of sewage; I could make it so that all the entrances are normally underwater and the PCs would either have to make Swim checks to get in (possibly risking disease) or hunt around for a drain.

One puzzle I had already come up with was a secret door leading into the lower level of the ruins, and I think I will go with the "series of trapped holes" for triggering it.

[♣♠Magic♦♥]

Go play Legend of Zelda, Majora's mask.

Or look up a play through of the water temple of said game.

[SmiloDan]

I like to use a metallic grate on the ground covering a pit with the hinges near the wall; open it up and It makes a ladder up to a secret door.

There's the classic series of levers opening and closing grates and portcullises. They can be marked with "Runes" that indicate which ones are safe and which ones are traps. The "Runes" with 4 lines (#, XX, <>, M, W, L7, etc.) are safe, and the runes with 1 to 3, 5 to 10 lines (can goblins count that high?) are traps.