Spot No Evil, Listen For No Evil, Search For (etc.)

Your Knowledge Arcana check, your Spot checks, and your Listen checks, all go nowhere.

You do need Balance checks, but fairly low DCs, and you can take 10 when you are not being threatened or distracted. (Hee hee hee)

The water is cold along your ankles, and it feels dirty. It may be mostly rainwater, but it's still slimy with dirt. It's dark, too. It's muddiness could easily hide something.

You step out to the other side and move towards the low-hanging pipes and stuff that obscures that corner. Castille easily spots a human-foot-sized depression in the dirt on the catwalk. But there seems to only be a blank wall...

(Castille needs to make a Search check, he gets a +4 circumstantial bonus on it.)

It is very wise of Kaspar to keep an eye behind him, especially since your Move Silently checks weren't so hot. (I rolled them for you.) A dark blob comes swimming over from one end of the pipe. (The grates will stop people your size but not necessarily something long and wriggly or jellyfish-like.)

His darkvision easly picks up the movement, and then he sees three long tentacles snaking out of the water and reaching for him...

Roll for initiative.