Gimli was allowed to go to Valinor despite not being a ring bearer. Is this explained in detail or just with the one line "for his love for Galadriel"?
There's not much detail about this aside from what's said in Appendix A to Return of the King:
We have heard tell that Legolas took Gimli Glóin's son with him because of their great friendship, greater than any that has been between Elf and Dwarf. If this is true, then it is strange indeed: that a Dwarf should be willing to leave Middle-earth for any love, or that the Eldar should receive him, or that the Lords of the West should permit it. But it is said that Gimli went also out of desire to see again the beauty of Galadriel; and it may be that she, being mighty among the Eldar, obtained this grace for him. More cannot be said of this matter.
And Appendix B:
Then Legolas built a grey ship in Ithilien, and sailed down Anduin and so over Sea; and with him, it is said, went Gimli the Dwarf. And when that ship passed an end was come in the Middle-earth of the Fellowship of the Ring.
And Letter 154:
But in this story it is supposed that there may be certain rare exceptions or accommodations (legitimately supposed? there always seem to be exceptions); and so certain 'mortals', who have played some great part in Elvish affairs, may pass with the Elves to Elvenhome. Thus Frodo (by the express gift of Arwen) and Bilbo, and eventually Sam (as adumbrated by Frodo); and as a unique exception Gimli the Dwarf, as friend of Legolas and 'servant' of Galadriel.
There are a few things we can deduce from these brief comments:
- It's notable that "it is said" that Gimli went to Valinor, and that the main text (from Appendix A) is very non-committal on the matter. It may well be that Gimli didn't actually go to Valinor after all.
- The Letter text treats it as if it actually did happen, and notes that Gimli was "a unique exception".
- The Letter text also notes that this is granted to mortals who have played a significant part in Elvish afairs, thus ignoring the reason (very explicitly stated in multiple other places) why Bilbo and Frodo went: for healing.
- It therefore seems that we shouldn't take the Letter text too seriously; it may well be a passing idea that Tolkien had but which is not in accord with what he wrote elsewhere.
I am going to belatedly provide a nitpicky answer:
Gimli did not go to Valinor.
Neither did Frodo, Bilbo or Sam.
They went to Tol Eressëa, where presumably they would live out their lives, Galadriel's song "Namárië" notwithstanding.
Somebody who has the Letters handy may even be able to quote verse and chapter, nagging in the back of my mind, where Tolkien stated that. Even something about the Noldor generally only moving to the Lonely Island, possibly Tirion or Alqualondë.
We can speculate that they were permitted to briefly visit Valinor and have something like an audience on Taniquetil with the Valar. Get a nice pat on the head for defeating Sauron. Maybe Gandalf, reverting back to being Olórin took everybody on a visit to Lórien. Who knows?
It's been a gripe of mine for a while here on SFFSE as it's generally conflated: Valinor is the lands of the Valar in Aman. It's not "the West" in toto.
The only reason Manwë spared the last mortal being who came to Valinor uninvited (Eärendil), is because he came on the behalf of Elves and Men, and didn't come for his own personal deeds. Gimli coming to Valinor because of his attachment to Galadriel would therefore be a personal deed, and therefore he would not be allowed to step into Valinor, and should he do so, Manwë would have killed him. I think this was just Tolkien's way of adding some additional closure to the story, in order to ensure readers knew that the fellowship lived happily ever after as readers anticipated themselves. Therefore I agree with Marakai that he didn't travel to Valinor, at most Tol Eressëa, and that this mention is purely a concluding device for Tolkien to add some additional closure.
According to all that's been said and done, one must assume (an educated assumption therefore) Gimli went with Legolas to the West, regardless if to Valinor or one of the off-shore isles. The "West" has always been a place of paradise and everlasting, this would include the Islands off the coast of Valinor, otherwise, why even go when you can live in Middle-earth to the same age, AND among friends and family and familiarity? It would not make sense to go to another land and die there at the expected age, without your people in full comfort.
Did Gimli go because of the beauty of Galadriel? While he loved her it would seem that would not alone grant him to live in the West. He went because of his bond with Legolas and that he was involved in the Fellowship, closely connected to the wishes and wants and needs of Galadriel, Elrond, Gandalf, all Elves or West-sent.
It is very clear both Bilbo and Frodo left Middle-earth for the undying lands, on Elvish ship, which is stated in the books. They were accepted because they were "ring bearers" namely, but also part of the same Fellowship Gimli was. The healing was simply part of the package, or part of life in Valinor or the isles.
Sam's leaving Middle-earth was not an invitation, and here is where it can get grey. The Valar could not change the laws or rules their God had created on the lands, and mortals. Mortals could only live for a while in the West.
But what of the isles off the shore of Valinor? What we have are NOTES Tolkien had, notes that were likely unfinished ideas, theories. It must be said that Bilbo, Frodo and Gimli, were INVITED to go and live in the West. In the books, The Silmarillion, The Hobbit, The Lord Of The Rings, we are not told any direction on how to interpret what would become of them had they been invited, accepted as Live-among-us type, which should lead us to believe they were GIVEN a gift, not to go there and die even with an added 50 years, and for what(?), but to live among Elves as immortals.
We have the books, notes which were likely not finished, and reason to go along with. As it goes in this story, there are always exceptions to rules, or new or different ways of seeing something, as Tolkien kept writing. I must believe according to all I have read, the three invited guests had to have lived as immortals in the West.
As for Sam, he was indeed a ring bearer, but he was mortal and not invited. Or, was he, as ring bearers have the right of passage. Had Tolkien lived ten or fifteen more years, we may have had more clear answers. Gimli, Frodo and Bilbo therefore, for me, lived in the West for ever, while Sam is a question. But why go only to have Frodo and others see him die. It doesn't make sense. All who are welcomed in Valinor or the Isles therefore should be granted life forever.