ASK him questions? Asking is also stimulating to his mind and his spirit...even if it's about the past.... ask things you never thought you could ask before? Who knows? He might just give you answers. But, if you don't ask? You will never ever KNOW about a whole lot of his past and thus yours.
Better yet? Make it a 'tell me' sort of project? About his growing up, his getting married, getting a family and on with life? It is 'ENGAGING' and can let him tell you all about him that he wants you to know.... IF you show the curiousity and give him the opportunity. Bring a recorder along to record his words for your children. Words on a page don't have the weight of words spoken. Also? You mite be surprised a bit too [about some things?]! Don't show shock, just an 'OH WOW' sort of response? To any admissions. Besides? You can always play it and have him 'near' you later....
It gives your visits a purpose, and also gives HIM some purpose & to look forward to? ..think on that and do what you feel best, if you can.

AND, yes, the trips to the facilities are the most distressing and dehumanizing aspects of being in rehab? [Been there, done that! Hated it!!!] It really depends on the nurses that you get? The good ones are often not appreciated. IF you see a nurse take good care of your dad? Tell the case worker? If your dad complains about 'someone' find out who it is, and also complain! Good care is hard to find in any country! Thing is they hire cheap and pay cheaper? So...you MUST recognize the good ones! In your case, it's your dad, next time? Could be YOU? It was me and The STAFF knew I wasn't gonna take any gump in any shape or form! When I was done w/them? And I'm not done yet!
I've also had two in-laws in long-term re-hab of the kind one does not exit from? That's been gut wrenching, but staffs were super and I'd always tried to let the staffs know that I appreciated everything done! Rehab was 700 miles from my home and it's not like I could visit weekly...so their reports were welcome news!
I hope this helps? And doesn't confuse things... I will put my mind to hoping that your dad can and does recover to a good degree! Don't be afraid to ask questions, as there are many here far more wise than I am! 's! - j