Near Badalona there’s a good hill to trek that can be accessed by bus from Badalona. You can catch a bus and get off at the Hospital Universitari Germans Trias i Pujol or just ask for bus to Can Ruti Hospital.
The trek is about 2 hours and a half and it’s a loop, so it’s easy to come back into town if you want so.
Since it’s summer and most of us might feel a bit thirsty, there’s a nice fountain in the lower part of the trek close to the hospital.
The views speak for themselves so have a look at them.