Exiting ATH on a TATL in the summer can be a mess. Some TATL flights leave from gates C in the satellite terminal, which is a 15-minute walk underground, entering from the main terminal. Document checks have a long line, and security lines are long, but there is fast track for the latter, and it is quick. However, passport control lines can be very long, a 30-40 minute wait, and there is no fast track or passport machines there. Thankfully, if your flight is boarding they will let you cut to the front of the line.

This video shows you around a bit gates C...