"The Lost City of Gold" is the 23rd episode of the second season of Gadget and the Gadgetinis.
It turns out that Nozzaire is a budding archeologist and author who had just written a book about the Aztecs. Unfortunately, nobody's coming to his book launch except Gadget, with news from General Sir. A recent earthquake in Mexico has unearthed the entrance to the lost underground Aztec City of Gold. Rumor has it the Aztecs hid their "Crown of Invincibility" in the city and it's a prime target for M.A.D., so W.O.M.P. has to find it before Claw uses it to become unstoppable.
Gadget, the Gadgetinis, Nozzaire, and an archeologist descend into the city while Penny's left back at their base camp since it's too dangerous for her to accompany them. She overhears assistant archeologist Ron Limond talking to Claw about how he has found and hidden the map to the secret entrance and shortcut tunnel that avoids all the traps Gadget and co. will face. He heads off to the city and Penny breaks into his safe to find the map, but unfortunately, Ron returns unexpectedly to pick up the crowbar he forgot and catches her. Ron forces Penny into the secret entrance tunnel and beats Gadget to the underground city's treasure vault. Ron chains Penny to the stone alter below the statue holding the mystic Crown of Invincibility and plans to leave her there since he's sure help will never arrive. However, despite Ron's expectations, Gadget bumbles his way past the traps and the living golden guardian idols into the treasure room. While Gadget is accidentally getting the crown off Ron, the Gadgetinis use their laser fingers to cut Penny's chains and she leads everyone (except Ron who won't abandon the treasure) back through the secret passage when the underground city starts to collapse.