Depending on your experience in C, the text editor in C tutorial [0] that was posted here recently may be good for you. There is good discussion in that post of other similarly sized projects as well.

[0] https://news.ycombinator.com/item?id=14046446

Since this comment gained traction, here are some better examples of what I meant by dumbledore's office:

A romp through approaches to generative adversarial networks described as if they are realms in a Tolkein world. https://news.ycombinator.com/item?id=20251308

(This week's) complete guide to building a terminal text editor from scratch in C which gently holds your hand at each step: https://news.ycombinator.com/item?id=14046446

Stumbling down the root domain of the above link leads you to the collected archive of _why_the_lucky_stiff, a hacker artist who created technical documentation as if it were a work of literature, animating and writing songs about ruby in a unique aesop meets kaftka meets neutral milk hotel style, and who then suddenly disappeared and deleted his whole internet persona, transmitting a 96-page oblique missive years later as individual PCL files. https://viewsourcecode.org/why/

Someone documents how using the 30+ year old, tiny awk language let him do what all the latest fad big data tools couldn't https://news.ycombinator.com/item?id=20293579

Several posts this past week from natashenka's Project Zero blog led me to her passion project of being the world's leading expert in hacking tamagutchis, which read as part instructional and part love letter to digital pets http://natashenka.ca/

Even though I'm ostensibly in the same industry as retail brokerages, I've never understood their business models as well as I did when I read this thread https://news.ycombinator.com/item?id=20276551

Not to keep going, but just to have a less lame example than a couple introductory textbooks -- I didn't mean to imply HN as a surrogate class syllabus