If you really want to have fun, fly to somewhere else in Europe, with a stop in London... You can fly to London then on to wherever, and then back...
In the process, remember that anything less than 24 hours does not count as a stop... I've often leveraged that to get a day visit somewhere in route...
Just imagine how much of Europe you could see on an ATH-LYR-AGP... You could potentially get VIE-MUC-CPH-OSL-TSO-LYR, with the return LYR-TSO-OSL-FRA-ZRH-GVA-MAD-AGP... Just make sure you only stay less than 24 hours... and you can do it for 20,000 miles :-)