What to do in Minecraft if you’re bored?

I have been playing Minecraft for a long time and know this world like the back of my hand. But recently I’ve been getting bored with it. I’ve explored all the caves, built castles and farms, but now I don’t know what to do next. My friends have also gotten tired of it and switched to other games. It’s hard for me to make a decision whether to keep playing or find something new. I need advice or inspiration to rekindle my passion for the game. Please help, I don’t want to lose interest in this world!