Houdini for games is only getting better. Houdini Indie, Houdini Engine - really great value for all levels - hobby, Indie all the way up to AAA... as for Terrains, have a look at this MasterClass : https://www.sidefx.com/index.php?option=com_content&task=view&id=3095&Itemid=410
I don't have caves but they were at GDC this year and quite a few developers are including Houdini into their games. https://www.sidefx.com/index.php?option=com_content&task=view&id=3187&Itemid=226
You mean something like voxel sculpting software or something more technical that uses VDBs? Houdini have extensive voxel capabilities that can be used for terrain generation and other things. Very easy to create terrain with caves.
That's exactly what the same use I'd like Houdini for: build level pretty fast and cheaply. And it seems some small teams were featured for that very same reason so I guess my assumption was right. I should start playing with the Apprentice edition right away.