Standard ESL books often lack the depth required for true C1 mastery. The following specialized guides target specific advanced skills:

: A great choice for learners interested in academic and technical terminology woven into a compelling narrative. 2. Sophisticated Non-Fiction and Intellectual Deep Dives

: Perfect for mastering 19th-century sentence structures and formal lexis.

How to get your English to C1 level | LearnEnglish - British Council