Hakubutsukan Wakusei is a Japanese novel of 442,160 characters, with 18,384 unique words and 2,445 different kanji. Its difficulty rating on Jiten is hard, 3.6 out of 5. The full vocabulary list ranks all 18,384 words by how often they appear, and you can study them on Jiten or download them as an Anki deck.
Here are some of the words that appear most often in this media, as well as a sample of its rarer vocabulary.