Grok takes a closer look at the docks. There are in fact two rafts moored there, each one hewn from giant mushrooms and lashed together. Long poles rest on the docks nearby. John has a sudden flash of recognition. This is the stretch of river from his nightmare!
Nearer to the docks, Grok can feel a draft coming up from downstream, and the echos of the river coming from there sound like there is a large chamber. The only apparent way to reach that are would be by wading in or rafting upon the water.