As typical for a huge large park, Chapultepec also has a castle. The castle itself is not huge, but it has a really beautiful view and the interior is decorated with marble.
You can get there relatively easy on foot from the entrance (the one at the Reforma) of the park. So you basically walk in and then another 15 minutes I think and then you come to the gate from where you can walk up a short and slightly uphill but absolutely doable path to the castle.
The castle itself then offers some really beautiful views and a few rooms with marble and royal splendour.
Go or not? Personally, I found the castle quite beautiful and also liked the views, but would definitely put the castle on priority two or even three. Not because it’s not beautiful, but because it’s just not thaaat cool and Mexico City is really, really huge. So if you don’t really have time, I don’t know if I’d do it 😀