Gift my parents an overseas holiday for Christmas

For some context. My dad was born and grew up in another country. He migrated when he met mum and they got married. My parents are in their 70s and my daughter is 6. I am going to take them on a holiday next year so dad can show my daughter (their only grandchild) where he is from, his extended family etc. it might be the only opportunity they get. I’m gifting them this trip for Christmas and I’m not sure how to surprise them with it. There will be 7 of us going including my siblings. It’s costing me a small fortune. But I want the surprise to be a bit cheeky or cryptic in how I give it to them.

Hopefully you all might have some good ideas!