In the future humanity will (hopefully) have many great achievements. If you could come back from the dead to witness one of these achievements which would it be?

Many great things humanity may achieve might not be in your lifetime. Suppose you could come back from the dead to witness a milestone in human history which would you choose? Here’s the catch:
-You are only granted a 48 hour pass
-You cannot change anything or talk to anyone only observe
-You cannot return as a zombie and start eating peoples brains (unless your choice is to return to see a zombie apocolypse…if you consider that a great human achievement)