On our last day we fly back to Nairobi around 11am. However our international flight doesn't leave untill 11pm. Any suggestion on how to spend the time?

On the assumption you’ve not seen these before, David Sheldrick Elephant orphanage, Giraffe Manor or Giraffe Centre, Karen Blixens House

You could also talk to your last camp wherever that is about late checkout, which would get you a game drive and lunch at your last stop before you fly back to Nairobi, likely returning you around 3 p.m. You could then go to the foster parent visit at Sheldricks which gets out at 6, have a quick dinner somewhere and then head to the airport.

I agree with this and also, you could go walking around in the downtwon area.

There is :
1. Uhuru Park
2. Parliament Building
3. Kenyetta Mausoleum
4. The Kenyettta Square and a statue of the first President of Kenya in the centre of the Square.
5. Visit the Independence Monument.
6. Take your passport with you and go to the Convention Centre building at Kenyetta Square... pay a couple of euros and go to the

top of the building for great views, then at the top is a circular stairway where you climb 2 flight of stairs and now you are totally out in the open, now climb a few more feet up to the circular helicopter pad and you feel like you

are on top of the world and you have the most panoramic 360 degree views of Nairobi.

On your way to the airport , leave a bit earlier and stop off ( it is almost on the way) at the Carnivore Restaurant...... for some African Game meat meals. !!

I hope you are a big meat eater, because there is a lot of meat being bar-be cued !!

Sheldrick & Giraffe Center, as mentioned above.

Also Nairobi National Park if you're up for more game drives.
Nairobi National Museum and Snake Park
Home - National Museums of Kenya - National Museums of Kenya

Never been, but there is also:
Bomas of Kenya
Kazuri Beads if you like crafts.

Thanks to everyone for the great ideas.