The graybeards will point you to more Shout Walls. Just ask them and they'll mark a new one on your map. Some of them are easy to get cuz there outside and all you gotta do is kill the Dragon guardian. Others are long Nord ruins like Bleak Falls Barrow. I got one where I had to follow a ghost through the tunnels, and we ended up in a sorta battle royale with King Olaf.