It's a passion project of mine.

Meaning

It's a hobby or activity I'm very enthusiastic about.

Examples

• John: What are you working on these days?
• Alice: I'm writing a novel. <b>It's a passion project of mine.</b>
• John: That's amazing! How's it going?
• Alice: Slowly but surely. It's challenging but so rewarding. <b>It's a passion project of mine.</b>