One of the first orders of business upon reaching level 70 in Final Fantasy XIV: Stormblood is to unlock the two extreme trials.
To unlock them, simply head to Kugane and speak to the Wandering Minstrel at (X11.6, Y12.6). He’s near the Market Board where many players are gathered.
The Wandering Minstrel will present you with three options, the first two of which will unlock these two trials.
Susano EX and Lakshmi EX are considered challenging but more manageable than extreme trials in prior patches, the first of which is the easier of the two.
Note that these two trials aren’t available until level 70.