Well Cap Salou is a suburb of a larger town called Salou.
If you look on the Internet for thing to do in and around Salou then that will give you some ideas.
The nearest major thing to do near Salou is to go to Port Aventure. This is a sort of Disney complex with 3 hotels, a fantastic theme park, and a pretty good water park.
It is right on the edge of Salou and in fact you can walk from Salou centre to Port Aventura (it may be a bit far to walk from Cap Salou)
You can read more here:
http://www.portaventura.co.uk/
It can get busy during the day (like all theme parks) and hot but when I was there it stayed open till midnight and it was really nice to go there from about 6pm till midnight. They have a great firework display at midnight.
The water park is right next door and you can easily spend a day in there, with lazy river, flumes, slides and so on.