Amusng older grandchildren

For the first time this Easter I have had a problem finding something that all 3 older grandchildren want to do. To be fair it has rained pretty much solidly the last few days which makes it worse.They are 2 boys nearly 10 & 12 & a girl of 8. Girl no problem- still likes all the usual things & the younger boy is very easy going but the almost 12 year old started BIG school last September & is growing up fast. I have them to stay in holidays as Mum works P/T & they live about 30 miles away so it is easier for them to stay for a few days than ferry them back & forth.In fairness to older GS he is a really nice boy & not the complaining type but I just feel I should be doing more to meet his needs. Let's be honest- it won't be long before he will be old enough to stay at home & won't need to come here anymore & that will break my heart but I accept it will happen.
I LOVE having them but I'm out of ideas. Farms playgrounds etc. are too young for him now. Cinema is OK but that is only one afternoon. We can get to London by train for Museums etc. but that works out expensive & also they are SO crowded in school holidays. I can get away with a good walk maybe once.
He has spent most of his time on Xbox playing Minecraft with his brother the last 2 days- very happy to do so but I'd rather be dong something all of us together .
Or maybe I'm being unrealistic??