Segovia is famous for the Roman Aqueduct. The Aqueducts supposedly dates back to 1st or 2nd century AD. The structure at certain location is more than 5 stories tall, and is over 1 kilometers long. The entire structure was built entirely of blocks of granites without any joining mortar or clamps. Even after nearly millenniums, it is still in good shape. The Roman engineering is quite astounding. Additionally, there is an Alczar (Castle) with a nice collections of cannons and armors.
Avila is known as the walled city. Its located on a hill and is over 1 kilometer above the sea level. The wall has 88 watch towers and 9 gateways. Additionally, Saint Teresa was born here in 1515.
Below are photos from my day trip.