Great discussion of setting up Site-to-site VPN using only Cisco IOS routers
Configuring Site-to-site VPN is usually very challenging unless we are using tools such as the Cisco Meraki Dashboard. However, there may be times when you do not have the luxury of a cloud infrastructure and other management tools to simplify the needed steps that happen behind the scene. This is usually the case with Cisco Embedded Services Routers as they are often deployed in use cases where they may not even be connected to the Internet. :: dCloud: The Cisco Demo Cloud :: is a self-contained virtual environment, albeit accessed from the Internet.
Recently, I searched for a really concise description of implementing Site-to-site VPN using only Cisco IOS routers. I found the following Internet article and successfully implemented it using the dCloud demo / lab, "Introduction to the Cisco 5921 Embedded Services Router v1."