Brief correction --<br/><br/>The above-mentioned still happened, but I didn't register Ria's action.  So, here it is.<br/><br/>Since Ria has been given a heads up about the pit trap near her, she knows to look for it.  And good thing too, because she would definitely not have succeeded in detecting it.<br/><br/>The DC for pit traps that are known to the party but not physically denoted (like, with chalk or string or what have you), is going to be a DC 8.<br/><br/>(https://i.imgur.com/aZhC1dA.jpg)<br/><br/>Ria, you did not encounter, or rather, you did not perceive, any pit traps along the way.  From your vantage, by Iona's light, you can see another switch on the eastern wall.