You can either use a teleporter to get to the bunker (the Camp Sentinel View teleporter, on the west side of the island in the middle of the channel, on a ledge directly above the left Nest Tower as you approach the cliff, will bring you to Camp Eagle's Nest, where you can access the bunker) or it is also possible to fly above the anti-dragon shield and drop down in human form, if you find the right spot. The teleporter by the blind philosopher will be activated once you disable the barrier.
There is a separate teleporter system that lets you travel to different places within the fjords (each named camp something). There are also a couple more of the teleporter shrines there you are familiar with from earlier in the game. A prisoner in the bunker can tell you about the fjords teleporters.
There is no rush on the seeds quest, since that is a main plot quest and its solution isn't needed until you are ready to move on from the fjords, Sentinel Island and Broken Valley.
