Also cool. I opted for GPS because I had a spare Pi and you can get dubious but perfectly adequate GPS modules for $3 off of Aliexpress, it's kind of an impulse buy. I also picked up a MAX7219-based LED display for another $2, so it's also going to be an over-engineered desk clock for $15 + some 3D printed parts (the other $10 is for a Pi Zero W I had left over from a different project).