This is Machu Picchu
It's a pre-Colombian Inca site at the top of these mountains in the Cusco region of Peru. It sits 2,450m above sea level, and it's that place I'd like to visit 'someday'.
You can get there by railroad, or (and this is what I'd really love to do 'someday') you can spend 4 days hiking the Inca Trail to get there. Apparently it's not the worlds toughest hike, although it's not 'easy' either, especially because the altitude will really take it out of anyone not used to living/hiking at such an altitude.
I think it's the 'adventure' of it all. A hiking experience like that would be so different to anything I've ever done, and this beautifully mysterious place would be so unlike anywhere that I've ever been. And I imagine that after some incredibly difficult days it would give me a wonderful sense of accomplishment to finally reach the top and wander through the lanes of Machu Picchu (no doubt dodging the locals who will catch the train up to sell me souvenirs).
And 'someday' when I'd visit, I'd really like to combine the trip with a cruise down the Amazon before hiking the trail, and then finish with a snorkeling trip out on the nearby Galapagos Islands. Amazing!
Do you have a 'someday' place?