The Safe House is designed to protect your troops from enemy attacks.
When your city is attacked, hidden troops will not be injured, as you can hide troops for a maximum of 8 hours. 

Important Notes:
- You can recall them at any time, but there is a 5-minute cooldown for each recall.
- Increasing your Expedition Capacity will also allow you to hide more troops in the Safe House.
- You can unlock and build the Safe House when your City Hall reaches level 10.