All this talk of Black Ziggurats has me thinking about one of my favorite D&D supplements, Necromancer Games' (R.I.P.?)/Morten Braten's ANCIENT KINGDOMS: MESOPOTAMIA. This book is composed of two parts: a guide for adventuring in ancient Mesopotamia with notes about the world, races, classes, magic and religion; and a series of desert adventures culminating with a well-detailed massive lost city.
Sorry, did I say "adventures?" How about a fully realized mini-sandbox setting, "The Red Wastes!" This adventure section consists of several linked locations, all gently prodding towards The Lost City of Ibnath.
Although this is a 3.5 edition D&D product, the material within could easily be used with any previous editions (and I did use it for my short-lived 4e campaign...please don't judge me...). Every page is practically dripping with inspiration and the contents are very "Clark Ashton Smith-esque."
Plus lurking in one of the detailed adventure locations is one of my favorite all-time iconic D&D monsters...The Froghemoth! Now let me go on a little ranting aside here. Froghemoth's rule. Return to the Barrier Peaks. Monster Manual II. Necromancer Games' superb resource Tome of Horrors.
So which retro-clone contains stats for the Froghemoth? Remember that since it is featured in the Tome of Horrors one can easily use it as open-game-content with proper licensing. It's one of the iconic gonzo Gygaxian monstrosities. It's a giant frog..with tentacles...
...I don't know of any retro-clone publication containing the stats for the Froghemoth. It's not in OSRIC, or Labyrinth Lord AEC, or the Swords & Wizardry Monster Book, or anything else I can think of. (I believe it's in a Pathfinder product..but that's not an "old tyme D&D" version) Seriously...what's wrong with these jerks? No love for the Froghemoth? For shame OSR...For Shame!