Unreliable narrator tells story that may be about his trip to Venus, or his experiences of sex, or both, or neither. A quote from the book is “Loksvy termarind,” Forrest says, “glou incrabular mock” - google responded "About 1 results" and then delivered two result URLs. Most importantly, this isn't the book I want to read right now. Abandoned at 35% after reading for less than an hour.

Recommended by Bart, who gave it 5 stars and reviewed it here: schicksalgemeinschaft.wordpress.com/2017/08/24/beyond-apollo-barry-malzberg-1972/
Coincidentally, I was attempting to read it in Mainz, not far from his land of Belgium.
Not coincidentally, I enjoy reading his reviews much more than this book.