On 29th March, Derek Yu will release a 222-pages book about his famous game Spelunky which will cover all its development processes, some kind of extensive making-of article.

An excerpt is on gamasutra:
http://www.gamasutra.com/blogs/DerekYu/20160323/268710/EXPLORERGMK_An_Excerpt_From_the_Spelunky_Book.php

The Kindle version is available for pre-orders on Amazon US and UK.
The good old paperback version is currently only available on the publisher website:
https://bossfightbooks.com/products/spelunky-by-derek-yu

Really? Is that a game that's popular and intricate enough to warrant a book about it?

Don't forget that the original one was out in 2008, that's way before people got into the rogue-lite and procedural bandwagon. It may not speak to players but that can be interesting for devs in terms of designs and such.

Probably.