If you're looking for user friendly, then browser's back button should suffice, it's a known and expected behavior, and for one level navigation, it's what most users will look for.
Now, if you want to keep context, you could use a modal window, but that will also depend on the content you have for those services and also the kind of behavior you're looking to achieve. Since a modal is disruptive, then the normal flow will be broken, which could be good if you have a CTA (which apparently you have) but could be a bit overboard for service descriptions.
Another option could be as follow: when users go down a level (eg each service page), show them a different template with a simple navigation on top or left featuring all services as well as the "back to Services" link. This way, users will be able to jump between siblings without friction and keeping control of their actions at every time.
Please note the different approaches above should be tested, and it's highly recommendable that your first option is based on your specific business needs. For example: if your users are likely to be interested in one and only one service between all those you have, I'd recommend a modal or a page relying on browser's back button.
Likewise, if you want your users to browse all your services (which shouldn't be the case in most situations), then use a secondary template with navigation, or a modal with tabs