Standard cell
One of the many things a PDK contains is the standard cell library. This is a collection of all the analogue and digital building blocks used to build an IC.
Even though they look flat, they are 3 dimensional structures.
SkyWater 130nm examples
Here are some examples taken from the high density SkyWater 130nm standard cell library.
You can browse them all here
Inverter
XOR
D type Flip Flop
Course feedback
Having the formal verification part additionally felt nice, that I could have something that I know is going to be functional instead of just guessing for a long time and then looking at waveforms and then not knowing what hell I'm doing!