These boots allow you to teleport around corners and to places you might not see from your current point of view.
Feet Slot 85,000 gp
When you use a power to teleport, you can instead teleport twice as the same action. The total distance you travel with both teleports cannot exceed the distance you could have traveled with the original teleport. You could, for example, teleport to a corner, establish a new line of sight, and teleport to a square not visible from your starting location, so long as the maximum number of squares teleported does not exceed the teleport power’s allotted movement.
Power (Teleportation) Encounter (Move Action)
Teleport 10 squares.
Published in Manual of the Planes, page(s) 156.