Recently I've been trying to decide on some fun math summer reading on some areas of math which I have less experience with. I'm an undergrad studying mathematics with a focus in actuarial science, but my focus has prevented me from taking classes in areas of pure mathematics. I basically just want to get more familiar with various subjects, to get a better sense of what I like, in case I decide to go to grad school, and also just out of interest.
By the time I graduate, I don't expect to have taken any classes in the following areas: topology, (real?) analysis, and perhaps some other subjects that I have no idea about. What I'm looking for is an introductory book in one of these areas which is relatively short (preferably $<200$ pages), and not too highly-technical. Do such books exist? The books that I see suggested elsewhere seem like they will be too long for me to really have a chance to get through.
A couple books that I have read at least partially in my spare time are Lawvere's Introduction to Categories, and Lancaster's Curve and Surface Fitting. Books in a similar style would be great.
I'd prefer books in topology or analysis, but I'm definitely open to other suggestions. I really enjoyed my introductory course on number theory/group theory, a suggestion for a more in-depth book on the subject would also be welcome.
Apologies if this question is a bit broad or in the wrong place.