I've been to hundreds of cities worldwide. My favorite is an underrated European gem that's an ideal mix of old and new.

Helene Sula and her husband, Michael, moved to Heidelberg, Germany, when they had never been there before.

Courtesy of Helene Sula

• Helene Sula and her husband, Michael, have visited hundreds of cities across the world.
• Sula said her favorite is a lesser-known German city that feels like it's out of a fairy tale.
• She said she loves Heidelberg's rich culture, beautiful castle, tasty foods, and lively festivals.

This as-told-to essay is based on a conversation with Helene Sula...