As you explore the regions of The War Within and meet the allies whose Renown grinds you'll be (thankfully) sharing across all your alts, you'll also be discovering new obtuse currencies such as the Earth-Encrusted Gem. This thing is a low-fantasy transmog farmer's dream, but as far as where to spend it, you'll be running around like a Kobold without a candle if you don't know where to look.

You'll need to find the ensemble vendor Osidion within the Forgegrounds in Dornogal, located at the location shown on the map below:

So, just in case you made your way here without knowing: how do you get Earth-Encrusted Gems? Renown, of course! You'll get one Earth-Encrusted gem at the following Renown levels:

That's nine total complete ensemble sets from Osidion throughout your journey, and some of them are pretty choice. From full wizard-themed sets to low-fantasy mining dwarf attire, these threads are a nice counter to the flashier sets you'll get via gearing.

It should be noted that Earth-Encrusted gems are Warband rewards, which means you'll only be getting one across your characters at each of the reward levels above. That said, nine is a pretty comfy number, so unless you're a real Trial-of-Style-head, you should have your fill and then some by the end of the expansion.