Mathematician Benjamin K. Tippett's arXiv paper "Possible Bubbles of Spacetime Curvature in the South Pacific" is superb.
In 1928, the late Francis Wayland Thurston published a scandalous manuscript in purport of warning the world of a global conspiracy of occultists. Among the documents he gathered to support his thesis was the personal account of a sailor by the name of Gustaf Johansen, describing an encounter with an extraordinary island. Johansen’s descriptions of his adventures upon the island are fantastic, and are often considered the most enigmatic (and therefore the highlight) of Thurston’s collection of documents.
We contend that all of the credible phenomena which Johansen described may be explained as being the observable consequences of a localized bubble of spacetime curvature. Many of his most incomprehensible statements (involving the geometry of the architecture, and variability of the location of the horizon) can therefore be said to have a unified underlying cause.
We propose a simplified example of such a geometry, and show using numerical computation that Johansen’s descriptions were, for the most part, not simply the ravings of a lunatic. Rather, they are the nontechnical observations of an intelligent man who did not understand how to describe what he was seeing. Conversely, it seems to us improbable that Johansen should have unwittingly given such a precise description of the consequences of spacetime curvature, if the details of this story were merely the dregs of some half remembered fever dream.
We calculate the type of matter which would be required to generate such exotic spacetime curvature. Unfortunately, we determine that the required matter is quite unphysical, and possess a nature which is entirely alien to all of the experiences of human science. Indeed, any civilization with mastery over such matter would be able to construct warp drives, cloaking devices, and other exotic geometries required to conveniently travel through the cosmos.
I quite like the bibliography, too.
 M. Alcubierre. The warp drive: hyper-fast travel within general relativity. Class. Quantum Grav., 11:L73, 1994.
 W. Dyer. At the mountains of madness. Ast. Str., Feb-Apl 1936.
 W. Hawking, S. and G. Ellis. The Large Scale Structure of Spacetime. Cambridge University Press, 1975.
 S. T. Joshi. A private correspondence, 2012.
 E. Komatsu and et al. Five-year wilkinson microwave anisotropy probe observations: Cosmological interpretation. Astr. J. Supp. Ser., 180:330–376, 2009.
 M. Morris, K. Thorne, and U. Yurtsever. Wormholes, time machines, and the weak energy condition. Physics Review Letters, 61:1446–1449, 1988.
 E. Poisson. A Relativist’s Toolkit. Cambridge University Press, 2004.
 F.W. Thurston. The call of cthulhu. Wrd. Tls., Feb. 1928.
 B. K. Tippett. Gravitational lensing as a mechanism for effective cloaking. Phys. Rev. D, 84(104034), 2011.
 R. M. Wald. General Relativity. The University of Chicago Press, 1984.
 Note: Johansen’s personal testament is currently archived in the rare books section at the main library at Miskatonic University.While we have not yet been able to inspect them ourselves, academic consensus has it that Thurston’s summary is consistent with it in most details . Thus, the specific descriptions we will be referring to are Thurston’s, and not