There are many--one of which I'm sure you've stumbled upon whether by accident or choice.

The underground of the city is filled with intricate tunnel systems, some even going under the waterways, though a few passages have been... "blocked". Every entrance is guarded - that's how they knew which district we left the tunnels in. The tunnels themselves aren't nearly as heavily guarded.

As for the energy... half of it was diverted to their greenhouses and the barriers. The other half is charging a machine they've been working on, though we couldn't get a clear view with the little time we had before we had to escape.