Sol is right smack in the middle of Madrid. The area for bars is just south of the main square and metro stop. It is a bit of a tourist trap but you’ll find many nice tapas bars and venues with live music that although they are not the most unique places you’ll always have a good time.
A lot of bars are also open much later than the rest of Madrid. If clubs aren’t your thing and the local bars are closing this is the place to head!
Las Letras is adjacent to Sol and a lot less touristy. A lot of the bars here seem to be caught in a time trap from the 80s but there are a few good ones.