House of Secrets originally series ran for 80 issues between Nov/Dec 1956 to Sept/Oct 1966. Primarily a mystery-suspense anthology, the companion series to House of Mystery featured the adventures of modern sorcerer Mark Merlin, dual-personality anti-hero Eclipso and Prince Ra-Man the Mind-Master. The series was revived three years after its cancellation, beginning with issue #81; Aug.-Sept. 1969, with horror and suspense tales that were introduced by a host called Abel (his brother Cain, hosted House of Mystery).
The House of Secrets came to be the name of the actual edifice in which Abel lived. Mike Friedrich and Jerry Grandenetti explained its origins. The Sandman series (which featured Abel as a recurring character) later revealed that it existed both in the real world of the DC Universe and in the Dreaming, as a repository for secrets of all kinds.
Swamp Thing also made his debut in issue #92 (June/July 1971).