Ever since I took a tour once of the Kronos Gyros factory, I now instinctively ask Greek restaurants if they make their gyros themselves. More than 95% of them buy the frozen cone from the factory. Stacking up the slabs of beef, lamb and fat, then trimming them to fit the vertical spit can take a long time, and I'll bet there are only a handful of places still doing things old school. One of them is the legendary Parthenon in Greektown. Carving as elegant a slab of beef and lamb as you'll ever see, then serving it with tart, homemade tzatziki (cucumber-embedded yogurt) is one of the true pleasures of eating along South Halsted. Opaa!