If you could (do something), (which/what/when/etc.) would (clause)

This is a common way to ask a question that is purely imaginary. People ask questions like this to find out about a person's interests and personality in a playful way.

Here are several other similar questions:

If you could be any animal, which one would you be?

If you could visit any country in the world, which one would you visit?

If you could have dinner with anyone throughout history, who would it be?

When you answer these questions, your answer should start with "I would...":

A: If you could live in any period in history, which one would it be?

B: I think I would live in the Old West.

Questions like this are called "hypothetical questions".

a period (in history)

A collection of years in history that had some common them is called a "period in history". Many periods in history are well-known and have common names. For example:

• The Jurassic Period is when dinosaurs were alive
• The Stone Age is when people used tools made of stone
• The ancient Egyptian period
• The Industrial Revolution is the period when people started building factories and machines.
• The Ming Dynastyis a well-known time period in China when it was ruled by the Ming family.

Of course there are many others.

You can also call shorter and more recent lengths of time "historical periods". For example:

The 60's is one of my favorite historical periods.