There are a pair of cavern complexes on Heart that span into Eravian and Anadyne territory, respectively. And through these cavern complexes, which somehow occupy the same space despite being thousands of miles apart, there is another world. 

We will skip, for a moment, how two polycules of cavers made the first hesitating contact; and how a particularly large and glittery cavern finally came to host the delegations from Heart and Homerealm for the first official diplomatic contact. There is, of course, an Eravian and an Anadyne delegation.