Murkmire is a new chunk of story DLC coming to The Elder Scrolls Online (opens in new tab)that will let players visit part of the Black Marsh, home of the Argonian lizard-people. Jump to about the 13.30 mark in the video above and you'll be able to see what that looks like in action. The new DLC includes the settlement of Lilmoth, which will be familiar to readers of the Elder Scrolls novels by Greg Keyes, and looks as swampy as you'd hope.
Chris Livingston wrote up (opens in new tab) a demo of Murkmire he saw at Quakecon, where creative director Rich Lambert described it as "about fifteen to twenty hours of new story content, there's dailies, there's two bosses, there's a new dungeon that's coming along with it as well."
As well as being available to ESO Plus members and via the in-game store, Murkmire "will be available as a Daily Reward for the month of November" according to this blog post (opens in new tab).