After you've been all the way to the River of Fire and returned to the ferryman --
-- Thanos will meet you by the lift and express his displeasure at your tourism. He then takes the remote, and how is Nancy to get back to the Underworld?
Occupy yourself with surface dealings for a while -- talk to everyone, call your friends, and finish any puzzles up here you didn't do before -- and eventually, Niobe will show you another way down to the Underworld.
After you talk to Niobe in the Workshop, exit through the blue doors to find yourself back in the Judges realm. Turn right and take the ferry back to the lift.
See the box here? Click on it to discover a puzzle. Read to the end of this hint for a picture of the solution.
This is a fairly simple type of puzzle. Your goal is to connect all the circles so that each one has the number of connections shown by the number in its center.
So if a circle has a number 3 on it, it needs three connections to other circles. See?
You can have one or two connections between two circles, and you can only move up/down and right/left; you can't connect diagonally.
One way to attack a puzzle like this is to look for any circles that can only be connected one way. For example, if you have a circle with a 2 on it and there is only one circle that it can connect to, you know you need to make two connections to that nearby circle. A 4 in a corner will have to make double connections with both its neighbors.
Next, I generally look for the biggest number. That 6 in the middle is going to have to make double connections with at least two of its neighbors.
When a circle has the right number of connections, it turns from red to blue. That doesn't necessarily mean it's exactly right; it just means the number is right. You might have to undo some of your blue circles to make all the circles turn blue.
If you just can't get it, here's the arrangement that works: