This 75-page PDF, written by Philip Reed and Michael Hammes, provides the DM with 8 new demiplanes that can be dropped into any planar campaign. See the demo for one complete demiplane - 9-pages - from this release.
The demiplanes included in this PDF are:
* The Ageless Chamber
* The Astral Ship
* The Blackguard's Tomb
* The Bone Field
* The Burning River
* The Chiming Clock
* The Clockwork-Driven Lighthouse
* The Great Corpse
Also includes an appendix of 12 unusual planar gates.