Neil Patrick Harris has embarked on the ultimate adventure - except he's got no idea where he's going.

The How I Met Your Mother actor is currently on a cross country scavenger hunt put together by his partner David Burtka for his birthday.

The celebration began on Saturday with a surprise party for Harris - who will turn 40 on June 15.

Then on Monday, Harris was driven to Las Vegas, where he trained with Cirque Du Soleil performers at Shine Fitness.

When "How I Met Your Mother" wraps its final season next year, is trading fake New York for the real thing.

"It would be great to move the ring from my right hand to my left, but Prop 8 won't allow us to do that," says Harris, speaking of California's ban on gay marriage. "David and I have been soulmate-y since we first met."

"'How I Met Your Mother' is wrapping up its last season next year, and we're kind of at the end of a chapter in our lives, which will be in New York," says Harris. Harris continues, "Our plan is to reroute ourselves and have our kids start to go to school here."