The Royal Opera House is one of the best classical music venues in the world. Antonio Pappano, the Opera House's music director, is a singular and extraordinary force in classical music today. He's a dynamic thinker and performer, and his musical vision, along with the fabulous artistic leadership of other musicians and administrators, has helped make the Opera House a warm and inviting place for both new and more experienced audiences. It's a friendly, beautiful, welcoming place to see your first, fifteenth, or fiftieth classical music performance.
If you're in London, check it out: easy to find in the heart of Covent Garden. Regardless of your geographical location, read this article by the guardian detailing the newly refurbished building, and the outreach the organization does to reach new audiences:
https://www.theguardian.com/artanddesign/2018/sep/19/royal-opera-house-linbury-theatre-open-up-stanton-williams