Just published: Marco Baistrocchi, "Agarttha: A Guénonian Manipulation?" Theosophical History, Occasional Papers, vol. 12. This is a translation by Joscelyn Godwin of three articles originally published in Italian in Politica Romana in the 1990s, by an Italian diplomat. An "engaged" author rather than a scholarly one, but still worth reading.
The whole question of Agarttha and Guénon's Le roi du monde (The King of the World, 1927) is puzzling. In Le roi du monde, Guénon endorsed views about the existence of "Agarttha," a hidden subterranean initiatic kingdom, that were highly imaginative. Guénon did not always check his sources as painstakingly as is required in academia, but on no other occasion did he devote so much energy to something quite so unlikely. Why?
Baistrocchi provides a useful introduction to, and summary of, the problem. He also more or less excludes one possible answer to the question. Guénon can hardly have actually believed the imaginative accounts he endorsed in Le roi du monde. He knew, as Baistrocchi shows (p. 22 and passim), one of the main sources for the imaginative account of Agarttha, Louis Jacolliot's Les Fils de Dieu (1873). But... Jacolliot was writing not about Agarttha, but about Asgard, the abode of the Norse gods!
So what was Guénon up to? Baistrocchi's suggestion, that Guénon was joining in a conspiracy to combat the interest in Asiatic religion awakened by the Theosophical Society for the sake of maintaining public interest in Catholicism and Islam, seems to me unlikely.
The puzzle, then, still awaits solution. But at least one possibility now seems to have been excluded.