Any Fun Unique ideas For a Boys BithDay Party?

I have 2 sons Turing 5 and 8 In October. I'm looking to see if anyone has any neat ideas for a birthday party...I have already had a Halloween party with the fog costumes etc.They have went to the Boo at The Zoo and last year we rented a huge tiger blow up bouncer with games etc. We live on 8 acres of land but it is also hard to plan something depending on the weather. Does anyone have any ideas??? This year is probably going to be their last shared birthday party so I want to make it a good one!