To explore the Eastern Plaguelands World of Warcraft area, you will need to spend a few extra minutes plotting your route due to the large volume and randomness of the area. There are locations in all four corners of the map, including the newly added Scarlet Enclave where the Death Knights are located.
Explore the Eastern Kingdoms Guide
First of all, you will have to go a little south to Thondroril River (8.71) when you first enter the zone. Go east from here to the Marris Stead (22.67), then straight north to the Fungal Valley (36.45), and henceforth to Darrow Villa (38.86). To go Crown Guard Tower (39.74), then travel north from here to the Infectious scar (49.62) and to Corin’s Crossing (54.66). Go around the lake to get Lake Mereldar (57.76), and then head east until you are in the Scarlet Enclave (87.74).
Then travel back west to Tyr’s Hand (75.74), and then head north Stinking Scar (69.58) Y Chapel of Hope of Light (75.52). Go west and then north to get to the Eastwall Tower (69.48). Enter the Harmful Clear (76.35) east of here and then back north to Northdale (66.25), after which head north to get Zul’Mashar (66.8). Go west from here to get there Quel’Lithien Cottage (48.13), then west to Stratholme (26.10) and southwest to Terrordal (13.28). To finish, you must go to Plague Forest (28.25), and then Northpass Tower (56.24).
The end point of this achievement will be directly south of here in Blackwood Lake (47.44).
As you can see, the Explore Eastern Plaguelands WoW achievement takes a lot of time and a lot of attention not to miss any discovery points, especially since it would be difficult to track down and discover the one that was lost. However, when you have completed it, you will have achieved and explored one of the largest areas in the game.