The American is ready for a 3,753km challenge that in October 1996, when he was found to have testicular cancer, seemed out of reach forever.
"I was prepared to forget the sport. There was a very real possibility that I would have to forget a lot of things," he said. "I just wanted to keep living"
He fought through 1997, riding for "some fitness and fun" as chemotherapy and a brave heart kept his illness at bay. This year his return has gone better than he expected.
"I am surprised by this season. After my problems this spring in Europe I honestly thought that when I went back to the States I would never come back to Europe. There were a lot of problems, and adjusting back into the sport was rougher than I imagined. Then I reconsidered, refocused, and it worked well."
Armstrong returned to win the Tour of Luxembourg and was fourth in the Tour of the Netherlands last week.
"All I had wanted to do was to ride and finish races. Then I started to win. I had no idea that this was coming. It was not in my plans at all."
His aim now is to be "very competitive" for the world road race championships at Valkenburg, Netherlands, from 6 October.
"If I race smart in the Vuelta [the Tour of Spain], and then race smart in the championships I think I can be with the best. I also would like to make it back into the top 10 in the world rankings.
"That's important to me because it shows a level of consistency which would nice to prove after my illness.
"Fighting cancer has made me more resilient. The Tour of Holland was a good example. There was solid rain, cold, and wind. In the past that would have bothered me. Now I just think `it could be much worse than this'."
The Vuelta, the last of the big three European tours, is part of Armstrong's build-up to the world titles.
"I am sure that there will be a stage win that I will go for, but not in the first half. I do not have my full condition just yet. It has been more than three years since I finished a three-week tour, the 1995 Tour de France. But I want to finish the Vuelta. I have to finish it.
"There are guys who want to make up for what they missed in the Tour de France," he said, referring to the four Spanish teams who quit the race in protest at the raids and searches for performance-boosting drugs by police and customs.
The Dutch team TVM, also interrogated during the Tour doping purge, are among the 22 squads who line up for today's opening stage of 161.7km.Reuse content