I play with an idea of running game set in Ulthuan. It would be elf-only game and it will be run as world-within-world aspect. Honestly speaking, I want sress this factoru very hard. But... can you give some ideas, how you would run such story?

One of the most important thing you should consider is how well your players are familiar with the details around the way High Elves live, their social values, their social structure, habits, etc, etc, etc... If they don't know enough about it and don't wish to roleplay accordingly the whole thing will quickly turn to a party of reskinned humans, living in a reskinned Empire. Also note that Ulthuan is the birthplace of most High Elves and each of them lives hundreds and thousands of years there, so walking around the island is not much of an adventure for most elves - most of it should be really familiar for them.

That's what comes to mind right now. I hope you manage to get the whole thing together and have a great time. Please post here to tell us how it went.

I have kicked around the same idea for quite some time. Are you planning to set the campaign/adventure in a time period other than the present? (By that I mean the current cannon of pre-Storm of Chaos.) I recently looked at the Warhammer Online resources and some of the maps and quests there might be of some use to you. If nothing else, much of the artwork could probably be useful if you like that style. I don't know that I have any suggestions on elven society or culture but I imagine that with a little work a campaign there could be just as fun as anything set in the Old World. If it is pre-Storm you could include Dark Elf agents on nefarious missions and the PCs are trying to discover and stop them. Perhaps in your world the Druchii are planning to corrupt the ley lines of Ulthuan in hopes of causing major problems for the Elves internally as they launch their attacks from the sea. You might also include some kind of antagonists from the coasts of the New World. Undead fleets or pirates subtly manipulated by Morathi to test the strength of the borders or act as a diversion for something else. Or you could use many of the cult/coven ideas from the old world and adapt them to Elvish deities and settings. (Slanesh may be the most easily integrated as he/she seems to be the Chaos power most associated with Elves.) In the first Malekith (spelling?) novel there was a slight touching on some of the chaotic/evil groups that had once infested Ulthuan. It would be up to you and your campaign style to determine if they still have any sort of foothold or if the Druchii are perhaps seeking to newly establish something like that. Perhaps secret assassins of Khain have been sent to eliminate key targets and are being sheltered by sympathizers. Elves do have long memories. Or maybe Malekith has designs on a certain artifact or magical device. You could also try something a little more ambitious that includes internal unrest such as social conflict and/or political intrigue. Depending on the scale that could be a very ambitious undertaking. In all things I would suggest that you get your hands on some of the older High Elf Warhammer Fantasy Battle books. There is quite a bit more fluff and background in them than the newer versions.

Anyway, just some random thoughts more than anything. But do keep us posted on your progress. I would love to see what you come up with.

Thank you very much for your thoughts and ideas. At least one was stunnig to me and have not came into my mind, this is why I love share ideas with fellow players/GMs. I mean, I have not considered elven longevity and it's impact on enviroment knowledge. This stopped me a while, but I suspect, tat there are still some undiscovered places or roads less traveled. Taking highly magical nature of Ulthuan under consideration, there is possibility of existence of magially hidden vallyes, pathways to distant places or even times?

Nevertheless, such chain of adventures will require some preparations.

First of all, I plan to set them little in future, after the Storm of Chaos. while elves helped coalition, the became disappointed and disgusted with humans, who spoiled fruits of victory, reverting to petty internal struggles, infighting and ways of treachery, double crossing and backstabbing. Seeing their efforts went nowhere, they Elves withdraw from Old World, intent to hold on in their island, proclaiming "Glorious Isolation" and offering rural kin a shelter in Ulthuan. (This will allow my players to choose between high and wood elves). I imagine we begin with withdrawal, to create strong contrast between grim, gritty and very low-life empire and clean, glorious, fairy-tale and high fantasy Ulthuan. Considering this, I will be able to by pass excellent knowledge of home turf and create some sense of mystery and discovery.

Second thing will be limited choice of careers. I guess I can turn it into an advantage, creating a special kind of game, as there will be no witch hunters or ratcathchers!

Third thing is, in my cyrrent campaign I have two wood elves and humans, perhaps I'll include hints of incoming withdrawal and retreat in adventures?