The next day, everyone is let out of work at noon to rehearse for the Singing. While Lina is chilling by herself, Doon runs up and grabs her, saying he found the place on the riverbank they were supposed to look for.
Since everyone's gathering for the rehearsal, the two of them sneak into the Pipeworks.
They find the rock marked with an "E" (for Exit, duh) and when they look around, then find a ladder leading down to a ledge next to the riverbank.
Despite the fact that it's scary to climb down a tiny ladder over a big roaring river, they both go for it. They find themselves on a ledge, which connects to a hall.
At the end of the hall is a door. They open it using information from the Instructions on where to look for a panel.
It's dark inside, but they find two boxes and bring them back out to the light. One is labeled "Matches" and the other "Candles." Neither kid knows what they are, but through enough fiddling around, they figure out that the matches create fire, and the candles can hold the fire.
Using the light from the candles, they explore the room, and find a thing called a boat and things called paddles. The next room is stocked with equipment. It's all kinds of awesome.
Interpreting more of the instructions, Doon and Lina realize that the boats are something they're supposed to use to travel on the river.
And that can only mean one thing: the river is the way out of Ember.