The CPU itself? For example, implementing a toy CPU is much much closer to how an actual, non-FPGA CPU works than, say, an emulator. But really anything done on

The CPU itself? For example, implementing a toy CPU is much much closer to how an actual, non-FPGA CPU works than, say, an emulator. But really anything done on an FPGA should teach you some portion of gate-level logic (yeah yeah, there's LUTs and other specialized cells instead of gates, close enough). And staying above physics, that's how computers work.