I'd be happy to help create a warm, inviting description for your Hiking session! However, I don't have access to the data from the fields you mentioned (12KM and the other field). If you could share what information is in those fields, I can craft a perfect one-line description that incorporates those details along with the title and the fact that it's free and open to all.

💧 Bring water, 👟 Wear suitable sport shoes, 🧢 Wear suitable clothes, 🎒 Carry a small backpack, 🌞 Protect yourself from the sun, 🧥 Bring layers, 🚫 Stay on marked trails, 📱 Carry a phone

No other specific details provided for this activity, which means you can just show up at the meeting point without further instructions.