How to Travel to the Removed Portal Locations in Patch 8.1.5

Caverns of Time, Kalimdor

The Uldum portal, added in Cataclysm, is still intact. Take the portal and fly east.
Take the Shattrath portal from the Stormwind or Orgrimmar Portal Rooms, go to the World’s End Tavern, and speak to Zephir to reach the Caverns of Time. Requires Revered with Hüter der Zeit faction.
Use Extrem sicherer Transporter: Gadgetzan to reach Gadgetzan if a Gnomish Engineer.

Dalaran Crater, Eastern Kingdoms

Alliance players can take the Twilight Highlands portal from Stormwind, which is found in the northeastern corner of the city with the other Cataclysm portals.
Mages can teleport themselves via Alter Foliant der Teleportation: Dalaran, picked up from Scarlet Halls.
A Mage with Alter Foliant der Teleportation: Dalaran can purchase Alter Foliant des Portals: Dalaran from Endora Edelhaupt in limited stock! If you don’t have the teleport book, you cannot buy the portal book. Should you take this Mage portal, use some sort of slowfall as you will end up in the air after taking the portal.
Druids can use Traumwanderung to port to the Hinterlands.
Rogues with Die Schatzkammer can acquire Schriftrolle der Teleportation: Rabenholdt to teleport to Ravenholdt.
Paladins can get to Lights Hope Chapel in Eastern Plaguelands by going to their Class Hall, the Sanctum of Light, from Legion Dalaran. The portals are located in Greyfang Enclave (A) and Windrunner’s Sanctuary (H).

Hellfire Peninsula, Outland

The Blasted Lands is a short flight from Stormwind, for Alliance players.

Karazhan, Eastern Kingdoms

Alliance players can fly from Stormwind or talk to the new NPC outside the Mage Tower, (NPC #150122), to port to the Blasted Lands
Teleport to Karazhan with the ring Violetter Siegelring des Großmagus, obtainable after completing Knochenarbeit from Return to Karazhan.
Druids can use Traumwanderung to port to Duskwood, close to Karazhan.
Find a friend with Atiesh, Hohestab des Wächters!

Vale of Eternal Blossoms, Pandaria
Fly southwest from the new Jade Forest portal
If you ran Challenge Modes in MoP, you may have some old teleports to the dungeons. Several are located in central Pandaria.

Wyrmrest Temple, Northrend

Simply take the Dalaran portal in the Stormwind or Orgrimmar portal rooms, then fly south.
Druids can use Traumwanderung to port to Grizzly Hills, close to Dragonblight.There are several teleport items to Dalaran, notably the Ring der Kirin Tor ring series sold by Harold Winston and Jainas Medaillon as a Shadowmourne reward.