Dark Ages achievement
After KarMann found a remarkably well-placed geohash while the old Wiki was out of commission, he found that he could have gotten another achievement or two if he'd been able to read the Wiki before setting out. (Yes, he did do some dredging about on the Wayback Machine, but that's rather more awkward to find arbitrary information on.) By coincidence, DanQ started up this NuWiki just a day or two later, and the rest is history. And history means Dark Ages. Geohashing was harder during the Wiki's absence (not to mention the persistence of geohashing almost 12 years into it). Let's make an achievement of it.
Criteria to obtain achievement
The usual proof of an expedition taking place on a date after the old Wiki was shut down due to the PhpBB problems, and before NuWiki was brought into existence. The expedition does not have to be successful.
While it is unclear when exactly the Dark Ages started and ended, anything between 2019-08-31 07:01 UTC and 2020-01-29 15:02 UTC is uncontroversial. The Dark Ages may have lasted longer than that, perhaps from 2019-08-30 11:01 UTC until 2020-02-02 07:04 UTC. This is currently being discussed.