I dunno, Oaxaca seems pretty straightforward. oa is pronounced kinda like "ua", I guess, but midword x is usually a "hh" sound anyway so that's the only slightly weird thing.

Fun fact, the Spanish X used to be pronounced like the Greek χ, which is why Meχico, Teχas and Oaχaca are pronounced the way they are now in English (formerly like a "kh" and now like a "ks")