I’m not going to tell you about its incredible history, you have Wikipedia for that. I’m not going to tell you that it’s a UNESCO World Heritage Site (well,.. I just told you), or that King Alfonso VI of Castilla ordered their construction in the 11th century.
I’m going to tell you about the experience of seeing the walls. It’s possible that you are someone who doesn’t like to follow the typical tourist path when you go to a city. Well, the most typical thing to do in Ávila is see the walls, and if you don’t walk around the top of the walls like everyone else, you’re really missing out. Visit them. See them. Climb them. Walk them. Not just from the outside, but paying the 4 € free and walking around the walls. Do it! It’s an order!
Seriously, it’s completely worth it. It will take you back to another era and give you an idea of what a city needed to be able to survive those times. You’ll be surprised at how well conserved they are (which began back in 1596 when King Felipe II ordered restoration work done on the walls).