Looking back to my youth in Eastern Germany, in which I devoured each and every Lem book, I will never fathom how his novel "Wizja lokalna" ("Eyewitness Account") (1982) was able to make it past the censors of this communist state and could appear as "Lokaltermin" in 1985. In large part "Kurdlandia", one of the two antagonized superpowers protagonist Pirx visits on planet Entia, is the most biting satire about an ossified, bureaucratic political system having just one objective left - keeping up the pretense that the cadaver of their ideology is still alive (which the inhabitants are forced to do in a rather literal, and absolutely hilarious sense).
Now that the Eastern bloc has been long gone this part of the book is more of historic relevance. But another large part is an in-depth exploration about where a free society is headed when AI and nanotechnology converge, all matter is penetrated and controlled by intelligent subatomic particles and the resulting omniscient, omnipresent "ethosphere" is programmed to keep all its human inhabitants happy. For instance, by avoiding all physical harm before it can actually happen.
It's probably not too suprising that the citizens of "Lozannia" (the other Entian superpower, where this techno-social development occurs) are _not_ consistently happy, despite all optimization ("hedonization") efforts of their government.
And then there is the brilliant comical premise of the book: Avoiding interstellar armed conflict is difficult because any and all real strategic intelligence about other civilizations comes too late due to the speed-of-light limit - therefore humankind uses fast-forward simulations of history on other planets. Now these simulations outputted two diplomatic notes from Entia to Earth threatening military action unless allegedly misstated descriptions of Entia in Pirx' earlier reports (in The Star Diaries) would be corrected immediately. (Both Entian superpowers had done/were about to take this step independently. And boy was the Lozannian note cool - I remember laughing for minutes after reading that page.)
So Pirx boards his spaceship and flies to Entia again for a detailed on-the-spot investigation.
Finally, that voyage makes up another unique part of the book - to entertain pilot Pirx on the long and boring spaceflight, he has received AI-based simulated copies of several philosophers and writers: Popper, Feyerabend, Shakespeare to name a few. Interesting dialogue ensues (as you might expect, the bard speaks only in iambic pentameter).
So this book combines deep philosophical thinking with sheer hilarity. Hence, suitable for all ages, even though not too many readers will enjoy _all_ parts.
In a 1986 interview [1] Lem explains the background of the book. What really blew my mind when discovering this interview recently is _why_ he wrote it - not because of the cold war, but since he was worried w.r.t. the challenges he very clearly foresaw for the _next_ phase of human history. Around 1980, no less. This man was prescient.
Too bad no english translation of this novel is available AFAIK. But as Lem himself admits in [2], the text is a translator's nightmare.
[1] https://www.depauw.edu/sfs/interviews/lem40interview.htm
[2] https://www.depauw.edu/sfs/abstracts/a40.htm