I don't think there are any symbols that will do this for you easily, so you'll need to draw most of it. Thus you can just pick whatever style seems best to you for the look you're wanting to achieve.

As your initial drawing shows though, even a simple pit will give you a template from which to work with for this, although it may help to pick a spiked pit to assist in getting the descending pillar polygons to look right at their various angles. The wall lines alone help with those near the pit's edges, after which you simply need to adjust the angling as you work inwards. There's a spiked pit in the standard DD3 symbols, for instance. To make it rectangular, simply set different suitably-sized X and Y coordinates when you're adjusting the symbol's size. This will produce distortion (especially of the spikes), but as you're just using the symbol as a guide for drawing to, that shouldn't matter much.

The pillar polygons will need some shading applied to make it look like they're fading away into darkness (like the pit walls in your post here), which can probably be best achieved using additional polygons drawn over the "lower" parts of the pillars (try the darker Solid bitmap fills that have various transparencies built in), coupled with some edge fade effects to blend one to the next (you'll need to set up several extra sheets to get this to work well enough). It probably won't be quick or easy to do this, because you'll have to keep stopping and thinking about what to do next (I know I would, which is what I'm basing this on!).

If you get stuck, just ask again here. Or maybe someone else more technically adept will come up with a much more elegant, and swifter, solution in the interim!

Well, I'm still hunting for the connecting sewer symbols to let me create a sewer layout for Parchment City (hey, it says I can do this on page 1 of the PDF Mapping Guide for it!) 😉😁!

[At a not-so-wild guess, that's an accidental copy-over from the March Annual!]

And obviously shocked there's no wyvern statue 😉🐲

Yet 😁

Looking a lot better now!

Yes, I think the walls would work very nicely for ruins too.

If the stepped outer surface was full regulated, it would also work for buildings such as ancient Mesopotamian temples, which had deliberately constructed outside walls that had this kind of "vertical recesses" patterning all round them. I've had to draw these before, both by hand and on computer, and it can be pretty tedious for a larger building plan!

Yeah, as Don says that's not really an issue for anyone who's ever played Call of Cthulhu. Surviving long enough to actually get to that point, now THAT'S the tricky part 😉.

For the crystal city concept, it may depend exactly how you envisage it. For a large-area map such as the Dungeon Worlds Annual will let you create, you could perhaps repurpose some of the standard CC3+ overland map symbols, like glaciers or icebergs (though you may have to get creative about hiding what are intended as water lines for the latter!), and making use of the varicolor options to recolour other features - and also with CD3 house symbols, for instance, if you wanted to map the city itself, or parts of it, in more detail.

It's definitely worthwhile to take some time to look through all the symbol catalogues you have available, and make a note of any symbols that might work in such map creation, even if that's a long way from what the symbol was originally meant to be! As you can resize any symbol in CC3+, imagine too how it might look if a given symbol were larger or smaller, or a different colour (which you can set and see while you're browsing through each symbol catalogue that includes varicolor symbols).

Just as well Wyverns can fly 😎🐲

Today, I've managed more, and relatively speaking, things have moved on some way from that. This is with the CD3 rooftop bitmaps still showing:

and this is it without:

Clearly, there's still lots to do - the roofing needs adding over the lower floor extension and porch on the upper floor plan, for instance, and other items need adding and tweaking in places. Such as a scale and the labelling! Plus I've decided life will be easier to reorient the north direction than the floorplans, and have rotated the surrounding buildings (or now technically building blanks) to suit that.

At some point, I'll need to work up some notes to go with this for the Atlas of course, though the map has the sharper deadline, obviously. The observant may notice the grille in the cellar. The local ghouls like to use the fabulous sewer network to get about unseen, especially after they created tunnels between the sewers and the cemetery beyond the city's northern wall. The ambiance of this haunted house - I'm thinking now "Cloven House" currently - and the fact nobody comes near the place ordinarily, makes it ideal for their feasts!

OK, so after an hour of checking, downloading and reinstalling, I have the complete 2018 Annual installed (again...), and an identical problem to Julian's still. No varicolor bushes unless I load from the PNG files, as described already above.

Before I reinstalled, all four of the Japanese Temples FSC files had dates of 31/08/2018, and they all still do, so I can only assume they were never updated in the final (i.e. the one huge, ~2 GB, Annual download file for 2018).

Hopefully these can be easily redone to correct the problem, though I imagine everyone who owns that Annual except Sue (!) will then need to reinstall the updated version.

As you might tell from my frequent use of random options in my Community Atlas maps, I've been a long-time fan of such random design systems, for all they can need a bit of nudging sometimes to get things to work out OK. I've not used the 5E system as yet, though almost exactly 20 years ago (July-August 2001), I created a classic 12-level dungeon using the random system in the original (1979) AD&D DMs Guide, each level filling an A4 page of graph paper. All done by-hand then, however. I did make a start converting it to CC3 not long after I got the program, around 2014 or 2015, I think, but that was very slow going, as I hadn't the option then to scan the hand-drawn maps to trace in CC3.

Have to say that your map looks a lot more elegant and less cluttered than any of my old ones from that dungeon set, so the 5E system may be something I should experiment with in future, perhaps...