I can certainly provide some historical events that are often of interest to people:
The signing of the Declaration of Independence (July 4, 1776): Witness the birth of the United States and the signing of this pivotal document.
The moon landing (July 20, 1969): Experience the awe and wonder of humanity's first steps on another celestial body.
The day Nelson Mandela was released from prison (February 11, 1990): Witness the beginning of a new era in South Africa's history and the end of apartheid.
The signing of the Magna Carta (June 15, 1215): Be present during the signing of this historic document that laid the foundation for modern constitutional law.
The Renaissance period in Florence, Italy: Immerse yourself in the artistic and intellectual flourishing of the 15th and 16th centuries, interacting with renowned figures like Leonardo da Vinci or Michelangelo.
The discovery of electricity by Benjamin Franklin (June 10, 1752): Observe Franklin's famous kite experiment and witness the momentous discovery that revolutionized our understanding of electricity.
Ultimately, the choice of where and when to go would depend on individual interests and the desire to witness significant events or eras that have shaped our world.