You can't travel through the exact center of the Earth because it's a solid, extremely dense ball of iron and nickel called the inner core.

Here's why:

* Extreme Pressure: The pressure at the Earth's core is immense, about 3.5 million times the pressure at sea level. No known material could withstand such pressure.

* Extreme Heat: The inner core is incredibly hot, estimated to be around 5,200 degrees Celsius (9,392 degrees Fahrenheit). This heat would instantly vaporize any known substance.

Even if we could somehow overcome these challenges, here's what you would pass through on your journey to the center:

1. Crust: The outermost layer, relatively thin and composed of various rocks.

2. Mantle: The thickest layer, made up of mostly solid rock but with a semi-molten layer called the asthenosphere.

3. Outer Core: A liquid layer of iron and nickel, generating Earth's magnetic field.

4. Inner Core: The solid, incredibly dense ball of iron and nickel.

However, remember, even if we had the technology to travel to the Earth's center, it would be an impossible journey due to the extreme conditions.