The "thing" is a
blackrock detector, designed by the mage Kronos.
Construction of the detector began more than one year ago, when Kronos' apprentice
Wexton asked for help to gather the required materials. The people of Britannia quickly collected enough resources to start the construction, but after the tragedy in Haven all progress was halted when the Guild of Mages
withdrew all funding, fearing what could happen if another lode of blackrock was found.
However, construction resumed when the Royal Treasurer
Lord Francesco decided to fund the completion of the device...
Apparently, it takes a while to approve spending of royal funds, because nothing has happened since
[****BIG SPOILER AHEAD**** - don't read if you don't like spoilers!!!]
Last spring, a public test of the blackrock detector event (also known as the Mad Mage event) was performed on Test Center. When Kronos activated the blackrock detector, obviously everything went horribly wrong and a time rift opened in Moonglow. The time rift led to a "timeshifted" version of Moonglow (a copy of the center of Moonglow surrounded by the void) full of evil creatures led by the three Shadowlords. The Timelord also stepped out of the rift to assist the players against the Shadowlords.
Loot on the Timeshift creatures included new items like a Cloak of Corruption and a few others.
The Mad Mage event was never released to the production shards (probably EA ran out of time for the KR release, and the event was replaced by the Destruction of Haven which introduced KR), but according to Cal's letter (and Draconi's post) it is finally going to be released in March.
Probably it will be different from the version that was tested last year, but this can at least give you an idea of what you can expect!