Airman First Class Spencer Stone’s summer vacation in Europe did not begin well.

There he was in Lisbon, the first stop of what was to be a three-week trip with two childhood friends, and he felt like a vagrant. A medic at Lajes Air Base in the Azores, he had missed the last train to Rome and so spent the night with his head propped against a concrete pillar next to a closed-up shop outside the Lisbon airport terminal, hugging his backpack to himself.

The next day he managed to catch a flight to Italy to begin the trip of a lifetime, but not in the way he ever imagined. By the time it was over, Airman Stone and his two friends — Alek Skarlatos, a specialist in the Oregon National Guard, and Anthony Sadler, a senior at California State University, Sacramento — had foiled a terrorist attack, saved a trainload of people and received the French Legion of Honor.

Airman Stone, who is to arrive back in the United States on Thursday, survived a stabbing in the neck. President Obama personally praised the friends’ bravery; President François Hollande of France said they had given the world “a lesson in courage, in will, and thus in hope.”

But before the hero’s welcome, the international acclaim, and the Jason Bourne-like maneuvers, Airman Stone spent the first week of the trip straight out of the pages of Let’s Go Europe. As he recounted in a telephone interview on Wednesday from Ramstein Air Base in Germany, he wandered the cobblestone streets of ancient Rome — his first visit to the city — enjoyed Piazza San Marco and a gondola ride in Venice, bicycled through Berlin and sampled the nighttime watering holes of Amsterdam.