When Chuckie's toy Reptar gets lost in the Pickles basment, the Rugrats go down to find it, putting their own twist on the classic book "Journey to the Center of the Earth" by Jules Verne. - Description from Klasky Csupo
Trivia
Chas calls Eve's Plumbing, a play on the name of the actress Eve Plumb, who played Jan on The Brady Bunch.