Borderlands – Where is “The Not-So-Phantom Tollbooth”

This challenge is fairly difficult, especially for the Gunzerker and Commando, whose special skills aren't of much help. edit: it was pointed out in the comments that I misread one of the Gunzerker skill descriptions. I haven't tested it, but it appears that he has an ability that works much like the assassin's.

Zer0 has the execute ability in his bloodshed tree, which can cause knock-back into the whirlpool. Maya's phaselock can be used on enemies jumping over the pool (you can lure them into this by jumping across yourself), which will drop them when it wears off.

Everyone can get this achievement using grenades, but it's tricky. The best grenades for this appear to be vanilla -- they don't do too much damage to kill the bandits outright and they're explosive, so they blast people away from them. MIRVs don't appear to work too well, despite their explosiveness. The phaselock-like grenades would be better if you can get them to go off above the pool.

There is actually an Easter Egg in this area if you manage to get all five lights green. Apparently, the switches all start in random positions for each player so there is not one unique solution immediately available to you, although you can deduce the solution based on what light(s) each switch triggers:

• Lever – 1 & 3 or 4 & 5
• Switch on Wall – 5 or 2 & 3 & 5
• TV – 1 or 1 & 3 & 4
• Wheel – 1 & 3 & 5 or 1 & 2

For more details, here is the source.

In any case, if you are successful, the Splinter Group's leader "Flinter" will crawl out of a drain and fight you.