One would be the Victorian era in London, having tea with Arthur Conan Doyle and Bram Stoker.
The other would be to fill today's mystery of how the monks managed to create the Book of Kells around 700 AD and where precisely.
Out of pure fashion sense like to experience the roaring 1920s in America as in Europe and the 1980s.
Perhaps retracing my family line, discovering how and why one of my ancestors stepped into the French knighthood and another in becoming in northern Germany a dyke reeve (Deichgraf).
And there's one more but it's far from pleasant and only research reasons for my story and most likely will put my life at risk one way or the other; so far I've gathered from that historic person, Vladimir 3rd Draculea in the 1450s today's Romania.