I do not know what community colleges ares, but I'd believe gymnasiums are much more similar to high school in Finland.
In Denmark, Estonia, the Faroe Islands, Finland, Greenland, Latvia, Norway and Sweden gymnasium consists of three years, usually starting at age 16 after nine or ten years of primary school.-Wikipedia
In Finland, the admissions to gymnasiums are competitive, the accepted people comprising 51% of the age group. The gymnasiums concludes with the matriculation exam (Abitur), an exam whose grades are the main criteria for college admissions.
Gymnasiums here are like an extension to elementary school. Subjects are the same, math, history, literature, biology, english, etc... with few new more scientic courses available, such as psychology. Studying is more rigorous and 'adult'. Students are allowed to create their own schedules and choose which courses to attend to (in elementary school they are decided for you). At the end of the 3rd year you'll have to do the matriculation exam on several subjects. It's practically a large essay which you have to write under supervision. After gymnasium school you are able to apply for colleges. Or you can do like I did, and go to vocational school instead and learn a profession (I became computer technician), and then apply for college (I chose to study computer sciences).