In 'Journey to the West,' stories about alchemy appear in great numbers.

Literal

'Journey-to-the-West' [possessive-の] inside [at-には] alchemy [possessive-の] stories [subject-が] numerously appear.

西遊記 (Journey to the West) is one of the four great classical Chinese novels. 錬金術 (alchemy) is a Sino-Japanese compound. 数多く登場する (appear in great numbers) is a standard academic/descriptive phrase. ~の中には sets the scope: 'within (the work).'