Basically, the feature lets you save a map covering an area up to 50km by 50km to your device when you’re in an area with a data connection. Then, when you’re in an area without a data connection or where data roaming charges are expensive, you can access the map offline. The end result is similar to what I recommended yesterday, but Offline Maps is a much simpler way of getting there. All you need to use the feature is a Google account.
Unfortunately the feature isn’t available in Spain so I wasn’t able to try it out. You can see the full list of countries where it’s available here.
I look forward to trying out the Google Offline Maps feature on my next trip. Thanks to Latif for bringing it to my attention.