You create linked teleportation portals. Choose two unoccupied spaces, one space within range and the other one within 10 feet of you. A circular portal opens in each of those spaces and remains for the duration (concentration, up to 1 round/level), or until the caster wills it closed (as a bonus action), or concentration is broken. This is essentially the same spell as Arcane Gate, only the 'far' portal can be anywhere that one can clearly visualize mentally within range, and one can see through the portals to the other side, though one cannot cast spells 'through' the Gate. This means one can open the far gate on the other side of a wall, say, so long as one has seen that space or a good image of it, but one can't open a Gate and then start hurling fireballs through it.
The portals are two-dimensional glowing rings, ranging from 1' diameter up to 1' diameter per level of the caster. Unless specified otherwise, they hover inches from the ground and are perpendicular to it, but the caster can choose to orient the ring however he/she wishes. (An 'entry' ring on the ground in front of a charging enemy, paired with a 'downward' facing ring high above is a very effective tactic, as is the use of a Dimension Gate to gain entry to a treasure vault--provided that one has seen the inside of the vault before--or to lead an attack on a high-walled castle by bypassing the walls.)
A portal is open on only one side (you choose which). Anything entering the open side of a portal exits from the open side of the other portal as if the two were adjacent to each other. As a Bonus Action, you can change the facing of the open sides or their orientation to the ground.
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