Voyager 1 & 2 is one of my favourite human science achievements, not even so much from technology standpoint, as it's relatively simple compared to what we have now (although that's one of the charms), but just the fact that it's so far away, it still more or less works long after the scheduled mission end time, we can communicate with it and despite all the modern technology progress, it would take decades to catch up. Absolutely amazing and inspiring!