Once you finish the main book, there's a few free bonus chapters provided [1] that help you implement soft area lights, bounding boxes (AABB in this case), and texture mapping. Beyond that, you might be interested in the "One Weekend" series [2], which is all C++ but is mostly general enough for other languages. There's also PBRT [3] which is an open source textbook/documentation for the pbrt-v3 renderer [4], but this is beyond the scope of "small exercise" territory. Good luck!

[1] http://www.raytracerchallenge.com/#bonus

[2] https://raytracing.github.io/

[3] https://pbr-book.org/3ed-2018/contents

[4] https://github.com/mmp/pbrt-v3