Ok.
Yes but because of the time spent in describing the pipe there was certainly a "reasonable" expectation that it would be noticed.
The pipe was originally checked as an ambush site, or a trap. The players asked for greater detail about the pipe, and did a dungeoneering check.
They discovered
1. It was fit one person at a time.
2. It probably connnected with the citadel
3. It probably travelled in a direct route to it, but moving inside the pipe would be at half speed.
4. There was evidence that the pipe carried high pressure waste water out of the citadel.
5. it would take 3-5 hours to get to the citadel if they tried to travel inside the pipe.
Each point detailed above was given in response to a question. THEY wanted to know more.
Two of them decided it would be fun to go up the pipe. The other three did not. This resulted in a split party.
If it is reasonable that it would be noticed then it is not unreasonable to expect some action to be taken regarding it otherwise why have it noticed ?
It got noticed initially because a player has a passive perception of 24.
It was remarkable because
1. Its an distinguishing feature, compared to the otherwise barren rockface of the mountain.
2. It does serve a game purpose, just not the one the players imagined
I also find it verisimilitude breaking that such a regular dramatic expulsion of water is not talked about by the locals ie " Wow you should see how the moonlights sparkles through the ...." or " It's pretty alright pretty noisy and stinky"
Ok, this is a good thought.
There are several reasons why this did not occur.
The first is that there is a orc war going on. One of the party members is a half orc. When the party is in his compay, nobody wants to do anything other than stick a knife in him. However, there are reasons (which I won't go into) why he is still breathing.
As for your example, they did ask about the citadel,..but who's going to talk about the plumbing? It's like asking a Priest about the Vatican and getting feedback about its toilet facilities. They were informed that dwarves trained paladins there, that served at the watch, and that weapons were also made at the citadel (this information was used to correctly form the theory that pipe water was used to flush out waste, including slag, metal shavings and whatnot, which a simple check of water traces confirmed).
I only ever recall drainage/sewage/aqueduct/plumbing at all being mentioned in gaming as means of ingress or egress . This drain didn't need to be climbable to serve the purposes you've mentioned it serving.
This a mistake made by the players. It was just a pipe. It was still a good idea to check it, but it was a dead end. I don't care what they experienced in other games,..it has no bearing on this game and its unreasonable for them to expect it to.
to the people that mentioned "paintings" et al as being redundant if you follow this path to you I say a painting won't cause a party to split up, doesn't take 3 hours of game time to examine, etcetera.
I'm not sure I understand this. Exploring the pipe took 3 hours of the characters time (About 15 minutes in real time to resolve). The three PC's who refused to go in the pipe, seeing that the other two PC's were adamant about exploring the pipe, decided not to wait around, and continued walking up the path. Hence a split party. Did I address this issue?
If there is a garden filled with gazebos not each one nor likely any need sat in or burned down, in a forest you don't climb every tree. But put one gazebo or one tree someplace where attention is drawn to it that can't be explained away (as was the case with this drain) then as I stated in the beginning it is not unreasonable to expect an examination to occur.
The purpose of the drain was explained,...as a drain. Two players obviously imagined it was something more. Three players saw,...at best a drain, at worst, a death trap.
sorry editted to add
as an aside it's "intents and purposes"
and free parking is only supposed to be a free resting spot there is no "pot" you get for landing there.
Sorry, I don't understand this.