The Nexus is an interdimensional locality of the Tackleverse, that has been described as "a waystation". It consists of a multitude of doorways, this way connecting different dimensions to each other, such as Earth or Hell. The ghost of the recently deceased Eustace Boyce was brought to the Nexus via his self-built eldritch computer, where he was greeted by a mysterious entity called the Serene Wanderer. She seemed to be quite well-versed regarding the navigation in this place, and made sure that he ended up at his correct destination.
Coloured rectangles reminiscent of the Nexus doorways could also be seen when the apparition of Tim Jones' father Stan Jones (who died 20 years prior) was wandering through the streets after one of his conversations with his son. It turned out that Stan can actually travel through time too, with the help of a cane that he invented.
Somewhat Nexus-like imagery could be seen in one panel when Charlotte Grote talked about "piercing the eldritch frontier". She then proceeded to tell a story about her visit to an extradimensional fairy realm to Shelley Winters.