The Wizard can fight and defeat Greater Gods such as Lolth.
Other Greater/Intermediate Gods such as Io are involved with the creation of the multiverse.
Other Demon Lords (which the strongest epic-level adventurers are capable of taking on) such as Demogorgon can create shockwaves that affect the entirety of the Abyss as well as the Astral Plane as a side effect.
AD&D's
Manual of the Planes tells us that the Astral Plane coexists with the first layer of each plane, in addition to mentioning that each planar layer of each Outer Plane is infinite in size, while also mentioning the Prime Material, Inner, and Ethereal planes to be infinite in the same manner.
The Astral Plane is connected to all other planes within the multiverse.
The Abyss itself is considered to have an infinite number of layers, and it was mentioned previously that each planar layer is infinite in size (though in the case of the Abyss, some layers are finite).
There is also the Far Realm, a space outside the multiverse that is infinite in size and with an infinite amount of layers and containing "countless" entities, some as powerful as the deities themselves.
Topaz Crusaders are psionic characters who, at the end of their journey, destroy the Far Realm itself at the cost of their life. Other epic level characters should scale to this.