Númenor Ruins
If you love the ocean, the Númenor Ruins are the place for you. A ship leaves from a port in Gondor once a week, and you will spend around 5 hours to sail there, 5 hours there, and 5 hours to sail back (assuming good conditions). There isn't much of it left other than the edges of the dikes, but the remains there are impressive. The water is relatively clear on a calm day, so you can try to swim down to see the remains of the Númenor statues. Otherwise, you can stick to the dry land bits. To the right is a map of what the island originally looked like before the flood.
Because Númenor's History is relatively unknown, here is a video explaining the main points:
Credit: Bitterhand