Wanting to escape Limbo, Antoinette Core used alchemy to construct a portal, which can warp through and dimensions lower than the third. The image shown in the information box, is of Jane in season three, when she pierced a hole through two dimensions, rescuing her family from Deep Limbo.
Then, when Antoinette's unconscious body got near it later on, it subliminally unlocked the collapsed portal, temporarily opening it yet again.
Jane recreated another portal (traditionally in the Beach Cave) later on in the series, to pull her family through from deep limbo. It collapsed soon after it was created.
Much later, Mandy Sheer sent Mozart into deep limbo, when her robots used Antoinette's DNA to reopen the portal. They sent him through. Later, Mildred reopened the portal to save Mozart, and to throw in Mandy. Mandy and Mozart swapped, and all was good... For now.
Wanting to escape, Mandy hypnotized Po from Deep Limbo, and using his conjuring wand, he reopened the portal, pulling Mandy through. Mandy snapped the wand.
In season eleven, Roberta instantaneously conjures a new limbo portal using Ginger's alchemy. This new portal is easier to use, and allows simple access to Limbo, Deep Limbo, and even The Zeroth Dimension. Roberta opens it in the beach cave, just for tradition.