Most impressive staircases you've ever seen?

I just love the staircase inside of the Vatican Museums, as well as the 16th Avenue Tiled Steps Project in San Francisco. Though drastically different, they're both incredibly beautiful!

I have seen some, but the ones that stands out for me are at Sigiriya Rock Fortress. There are several other staircases at this place as it was built on top of a huge rock back in BC's.

The The Art Institute of Chicago has a beautiful and frequently photographed staircase....

Livraria Lello & Irmão in Porto, Basílica de la Sagrada Família in Barcelona, Capitoline Hill in Rome.

The one I had to climb (over 600 steps) to get to the top of Piedra del Peñol, Guatape in Colombia. Not that stairs were somehow impressive, but the way it was built into the granite monolithic rock and a beautiful view you get once you are at the top.

Huangshan Mountain, south of Suzhou, China. UNESCO World Heritage park, 60,000 carved stone stairs, some over 1,500yrs old. Hotels at top and in valley at bottom. Going up is a really tough 1-day trip. Coming down is doable but take knee support and aspirin, start early and you will be off by dusk. If you want to see/learn more, check this blog: http://rbtglennketchum.blogspot.com/2015/05/weekly-post-china-travels-since-1985-by.html posts #68-118.

In Barcelona, check out Gaudi's staircases at Casa Batlló and in the towers of the Basílica de la Sagrada Família.

In Rome, climb the famous Spanish Steps.

If you love the view from a cathedral dome, climb the spiral steps of the Saint Paul's Cathedral and the St. Peter's Basilica.

Stateside, the Gorge Trail at Watkins Glen has beautiful waterfalls, narrow trails, and a series of rustic stone staircases.

In Mexico, climb the steep steps of the ruins at Monte Albán

First thing that comes to mind are the stone stairs on the Aztec's Pyramid of the Moon and Pyramid of the Sun.

Selaron Steps in Rio de Janeiro is the one that I most remember!

The Selaron Steps in Rio de Janeiro is very cool with all it's colored teils and bohemian vibe.

This is where I'm going! The Devil's Cauldron in Banos, Ecuador. 

One I did recently is the Eiffel Tower in Paris France.  The line to take the lift is sooo long, that you better can take the stairs if you can, is good for your helth and you can stop at all times to watch the view when you go up.  Then you arrive to the 2nd level, to go to the top (1ste level), you still need to take the elevator (and another line of people).  There is no stairs to the top (that is allowed).

The same for the atonium in Brussels Belgium in the center of Europe, a must see.Atonium

Eiffel Tower

Also, checkout Santa Monica's staircases where you're likely to see "impressive" celebrities getting in a workout. 4th street stairs, Santa Monica, CA.

Tiger Temple, Krabi: the 1237 step pilgrimage to the footprint of the Buddha. The steps are rutty, in spots well off their original path, winding through trees sheltering generations of monkeys who don't mind letting we mere moral pilgrims know who really runs the show. Since recovering from the 2004 Boxing Day tsunami, the base area, gift show, snack area etc, has become a bit of a show. The top, however, and the views therefrom, are worth every sweaty step. 
Some pics here.

My most impressive staircase is served for people to go to heaven. 

"Stairway to Heaven" on the way to Batad Rice Terraces, the UNESCO WHS in Ifugao province, Luzon, Philippines.

I have seen two straircases worth mention. 

The Water staircase in the Alhambra gardens in Granada. It not made of water but the hand rail is has running water going along it. The sound it makes is so wonderfull, i could have stayed there for hours.

The other, is the main double elliptic staircases at the Château de Chambord. Two staircases intertoined one into the other. Apparently, the king didn't want to see much of the queen so they had one staircase each going to the same place but never seeing each other comming or going.

Hands down. The Loretto Chapel Staircase in Santa Fe NM. Look them up. They have a very mysterious story to them!