First Congratulations!!

I taught web design a few years back and would have been impressed if one of the students had actually taken the time to do something like what you've done.

In the sense of the teacher the only advice I would make is to clarify the "back to main page" on the third level (where the pictures actually are). I would have docked points for not going where it indicated. Maybe just put "Back."

As a web developer I would suggest consistency in your page naming like using all lowercase (Ex. bothpg_1.html). It bit me in the butt when I switched servers once. And don't pay attention to anyone that tells you how the future will be, unless it's your professor of course. Example, I was told two years ago HTML would be gone by now as a web language.

Knowing the requirements for the assignment might help you get the best feedback.

Anyway, great job on building a solid and well functioning web page!