""giant castle dungeons with bosses in them with fun new items" I guess this is Chocolate Quest (aka Better Dungeon 2), it did generate lots of random dungeons in the overworld. Botania is now only updating for Minecraft 1.7.2, so you won't find any 1.6.4 mod packs included it. I would suggest you to try Resonant Rise mod pack, it has Chocolate Quest, no Botania, but it's really fun to play." - number5