These is another terrain piece from Printable Scenery, cut into two pieces and printed on my Ender 3 at 0.2mm layer height in eSun PLA+. I printed it using Tom Tullis' terrain profile for Cura 5, but if I were to do it again I'd bump up the number of walls to three or four, as the columns proved to be quite fragile and broke off easily when I (repeatedly) dropped the pieces.
I began (after gluing everything back together again) by priming everything black, and then spraying a downwards zenithal white to define shadows and highlights. In retrospect, the zenithal spray could probably have been skipped, as the next painting step pretty much obliterated it.
I painted splotches of three colours all over everything: yellow ochre, burnt sienna, and Van Dyck brown, in roughly equal proportions. You can see the result in this photograph, and as I imagine you'd agree, at this stage it looks pretty awful. I used Maimeri gouache acrylics for this step, thinned down until they're quite liquid.
Once the spotty paint was dry, the next step was to over-wash everything with black.
This technique was originally developed for railway modellers' cliff faces and such-like, and it works better on plaster or similar absorbent material, as the paints and wash penetrate into the surface and the black wash evens out the tones a lot more. However, it still works on this unabsorbent plastic, if not quite as well.
Once the black wash has thoroughly dried, the next step is to dry-brush everything to knock back the darkness and bring out the edges to delineate the forms.
I used Vallejo VMC Buff for most of this, and then some VGC Elfric Flesh (a very pale off-white) to catch the upper edges.
After dry-brushing, I went over everything, stippling very thinned-down Elfric Flesh with a natural sea sponge, to give the weathered stone a bit of textural variation. Many areas got two or three layers of this treatment.
The terrain piece is usable just as it is, but a next step would be to add some moss and grass flocking in amongst the cracks of the paving and in various of the crevices.