You and your Guild Wars 2 [officail site] guildmates will get a secret clubhouse to hang out in with the Heart of Thorns expansion, as it reintroduces guild halls from the first game. They'll be a lot swankier this time around, involving a lot more work and giving you more to do as you build and customise them, as developers ArenaNet have explained in great detail following an E3 announcement. Eight chunky blog posts tell exactly what you can expect as a guild member when it comes to the new guild housing situation and how it now fits into the game's storyline.
Obtaining your new guild hall is a quest in itself. You'll need to liberate an ancient ruin of its Mordrem squatters before claiming it for team. At the launch of Heart of Thorns there will be two different styles of guild hall available, though there'll probably be more in the future. Two's enough to be getting on with for now. Especially since the customisation options seem so impressive.
Guild missions are also being overhauled and made available to new guilds right from the start. Since these are now your source of one of three guild hall upgrade materials, it would be unfair to keep them locked up until late game. So expect to be spending even more time with your guild mates, whether you’re at home in your guild hall or not.
ArenaNet are also adding guild teams to the game. These are five-person teams created specifically to fight in PvP arenas. The blog post promises this to be a "platform feature", with a greater variety of guild team adventures coming later. That itching feeling you have right now is the suspicion that Arenanet may be intending the enter the world of MOBAs with this new 5v5 guild team mechanic.
There's tons more information for you to check out ahead of Heart of Thorns nebulous release date. You can find it all over at the Guild Wars 2 blog. Specifically: