I am surprised nobody said November 22, 1963, then again that isn’t a past civilization, is it?
Mine would be pre-Christian Celtic Ireland.
I’d like to go back and tag along on Powell’s 1869 expedition through the Grand Canyon.
Of course, there is the possibility that such a request might take you nowhere! 
Even more likely if you requested the resurrection…
I’ve always been interested in what it must have been like in Cahokia. - say around 1150-1200 or so. Though it would be hard to choose among the many historical periods identified above, I’d probably go with Cahokia as a native Illinoisian.
I’d also love to attend an early meeting of the Royal Society in the late 1600s or so. Maybe meet up w/ Hooke, Newton, and others.
Man, so many things to choose from. Off the top of my head:
Tombstone, AZ, October 26, 1881
Philadelphia, PA, Independence Hall, September 17, 1787
35°1′38″N 111°1′21″W, about 50,000 years ago when the meteorite came down
Site of modern-day Chicxulub, about 66 million years ago when the dinosaur killer came down.
Bosworth Field, October 22, 1485
So many more…
Monaco … about an hour ago …
Arcetri, outside Florence, Italy, 1634 … visit with Galileo …
Depends on which Doper is reading.
But it matters a lot if he is the Messiah, the literal son of God.
It helps if you believe.
Like I said, I know others would choose this, so I won’t.
(Actually, I’m pretty sure there are some who would choose Auschwitz, perhaps to solve the mystery of a lost grandparent.)
The battles of Gettysburg and Shiloh are tempting, but I don’t know if one guy on the ground could get a really meaningful overall view of the event. They’re just too darn big. WWII’s D-Day could be fun…but there are actual living participants, so there isn’t too much point to it.
Might be fun to watch the Constitution vs. the Guerriere. (Monitor vs. Virginia was apparently fairly dull. Or how about Trafalgar! Or the battle of the Nile! Yum! I’m thinking of changing my vote to Trafalgar!)
The Inca Empire sounds a lot cooler than the Aztecs, at least to me.
I am mildly confused by people selecting locations that would get them killed given that the very title of the thread is ‘spend a day’, not ‘watch via magic’. Do you really think that standing on the spot that the dinosaur killing asteroid hits, or on the coast of Normandy on D-Day is going to be survivable?
I will admit to some surprise myself. But then again three relatives, the only ones I had involved in D-Day, managed to survive. If I was curious or interested enough I would consider taking a chance. Heck – even my Quebec thing carries quite a bit of risk of death.
Cätal Hüyuk or however the hell it’s spëlled, in Turkey, circa 10000 years ago.
Nice one!
Since the OP didn’t specify, maybe you don’t have to be there as human but still be you. You could be a bird flying around over the battlefield or the proverbial “fly on the wall”. But with all your human intellect in place of course.
However in the case of the dinosaur killing asteroid you would still be just as dead as the dinos.
I would approach this more as a vacation than being in the thick of a historical event.
My choice would be Thera Santorini about 1600 BC, at the height of the Minoan civilization there. Just to hang out and eat and drink and soak up the sun.
Nevermind the Crucifixion. I want to record the Sermon on the Mount.
Stonehenge, circa 2500 BC, preferably on a solstice or equinox.
Athens during a Panathenaia festival.
Venice, during Carnival, 17th or 18th Century.
Athens in 390 BC, to see the complete and undamaged Acropolis.
Rome ca AD150, ditto ditto Forum.
Cahokia and Çatalhöyük also sound good.
For fun. 1930’s-1940’s. Somewhere between those times. The abundance of art deco, the clothing, the music, the atmosphere… It appeals to me for some reason. For a more educational experience, I would have to go with mbh’s suggestion. It would answer some questions and appeal to some curiosity.
The day before Atlantis sunk into the sea.
The atmosphere of the Great Depression and WWII?
The past is a dirty, smelly, diseased, violent place. I can think of several historical events I’d like to view remotely (such as seeing and hearing Senesino and Farinelli performing Artaxerxes in the King’s Theatre, Haymarket in 1735), but few I’d like to be there in person for.