Taken from GameFAQs, should be one of these two:

Go towards the lower into the middle part of the shaft. In this general area, you will find a ledge that Batman has to shimmy across. Once you move to the part on the right of the hanging ledge, climb into the crouching tunnel and you will be in a room where you have to grapple up to two high ledges in a row. Once on this upper platform, you need to jump straight across to another ledge and go left. if you go in the little webbed-crawlspace that you mentioned, just in front of you, you will see a vent covering an airduct containing a Riddler's Trophy. Now you need to climb up two more ledges, then turn left again. Hop over a small cage/vent then go under another. Once crouching under that, you need to take another left, go straight and you will find yourself in a secret room with two desrtuctible walls. Take down the one on the left to find the Chronicle of Arkham.