I apologize in advance if this is a very soft question. I won't be surprised or offended if I can't get a good answer.
One of my favorite things to do in my spare time, when I'm feeling analytical of course, is to evaluate integrals, both definite and indefinite. However, I've had little success here on Math.SE trying to find integrals that meet my criteria.
Either the integral in question will be way beyond the methods that I understand to evaluate it (typically using contour integration), or is so mind-numbingly trivial that I can't be bothered writing it down. I've scoured the internet for some interesting integrals, and I found the MIT Integration Bee, but those aren't really that hard either. There are some decent ones in my multivariable calculus textbook, but I'm starting to run out of those too.
Is there any specific place I should be looking for interesting, tough but doable without complex analysis? Specifically ones where we can evaluate through tricks like clever substitutions or exploitation of symmetry or changing coordinates, etc.