I was looking at statistics for prices of sold houses in a European country a few years back, and started digging around in the javascript of a local newspaper

I was looking at statistics for prices of sold houses in a European country a few years back, and started digging around in the javascript of a local newspaper that every month listed the local sold properties. Turned out in the API they were using from the central statistics provider, they just had "days=30" and "municipalities=[list]". They weren't even caching it, every user visiting the page was another (identical) request to the API provider. And sure enough, sending a request with "days=3650","municipalities=[{all of them}] gave me 10 years of data with every property sale in the country.