I've been thinking about going back to school for my bachelor's degree, and undergrad academic degree which takes 3-7 years.
That's exciting!  What kind of degree could you get?
There are so many options!  The bachelor's degree is the most common undergraduate degree.
What kind of pre-requisites do you need?  
That really depends on what you want to do.  For instance, if you want to go to a medical school for a degree for physicians, you could do science based courses.
Does it vary depending on the country you are going to school in?
Yes, for example, some countries use qualification frameworks, and a bachelor's degree could be qualified differently.