For an undergrad OS course, we had to build an OS from scratch. Part of that was doing the dance to get from real mode to protected mode. We had a bug in our boot loader that we were pretty stumped with; to solve it, we ended up hacking debugging printfs into the "CPU" inside QEMU and found the problem very quickly.
I don't want to be working at that level every day but it sure was a fun project.
I remember dumping registers to text-mode screen memory so that I wouldn't waste a register. Half of the result landed in the color values, so sometimes I couldn't read all of the value because it was flashing green on green. I prefered Bochs' Port E9 hack.
Oh, OS courses at the university... good old time. (Some participants complained that going from zero to bare-metal x86 was too difficult.)
I don't want to be working at that level every day but it sure was a fun project.