The third prueba tests on proficiency in written Spanish. This was actually my worst section (possibly due to lack of practice). I got a 15/25, or 60%, which is the minimum passing score for the DELE C1 exam. Overall, I believe this was most likely due to my lack of practice. I didn't practice writing any formal essays in the months preceding my exam (thinking that my writing was my strongest skill in Spanish), but I was definitely wrong. The DELE knows that people generally read and write better than they can speak and listen. As a result, they make the writing test more complex than the other sections. Don't get me wrong, the task and the writing prompts themselves are fairly simple. However, the grading rubric is pretty harsh. It's not enough to just write an essay that's coherent and correct. At the C1 level, you need to demonstrate sophistication in your writing style, using adequately complex vocabulary and sentence structures where they fit. I would say that the writing section in Spanish is probably similar to taking the SAT Writing section in the United States.
After the jump, I'll detail the couple of sections that I was given in this prueba.