Written by MSG Commander
After you've completed the Omega Tower, talk to Tessarosa in Vanessa's Lab. He tells you to explore the basements in Vanessa's Lab and the Energi Lab, and to look for a researcher who may have information on Legendary Weapons. The researcher is in the basement of Vanessa's Lab, but you should explore both basements in order to get all of the treasure.
I recommend you do Vanessa's Lab Basement first, and get all the Legendary Weapons.
Then, if you want to, you can do the Energi Lab Basement, although you don't need to do it in order to complete these quests.