When: Anytime after you collect the Voidwalker
Where: Dry Road Access Tunnel
Need: Voidwalker and Crossblade equipped

For reference purposes, lets say you just used the wormholes to transport to the Scalding Gallow, from inside the Vulgrim location go out of the little building and turn right to go towards the Dry Roads. When your in the tunnel with the cars take out the few enemies there and then go into the side room with the cronosphere and lever. Stand next to the lever and use the crossblade to trigger the cronosphere, flip the lever, then run under the door. Kill the enemy in there so he doesnt bug you.

Now look at the door, you'll notice there is a portal space in the middle of it, use the voidwalker to make that (charged) portal, then use the lever and get back to the original side. Then use the voidwalker to make a portal in the control room (portal space is on the opposite wall of the cronosphere). Use the lever and when the gate is raised you'll see a little ledge through the portal, go through the portal and zoom to the ledge, the item there is the Death's Blessing Enhancement, one of the 3 legendary enhancements in the game.

When used with the Scythe it converts damage you do to enemies into automatic health for you and increases the number of souls you get from enemies and objects.

Enjoy! :)

-Troy