Originally a mining settlement built by the East Empire Company, Raven Rock is the first place you are likely to explore when diving into Skyrim's Dragonborn DLC, as this is the port where you land after taking the Northern Maiden from Solitude. Despite being a small town, there is a lot going on in Raven Rock even without taking the main questline into account.
Although a lot has changed on Solstheim since it was a playable location for The Elder Scrolls III: Morrowind, it is still the same desolate, alien island that made Morrowind so memorable in the first place and is in stark contrast to Skyrim's white, frozen mountains.
Merchants
Although Raven Rock has many different merchants within its walls, including a general store, blacksmith, and an apothecary, they aren't so easy to find that you can just walk into one of their stores so easily. Unlike in Skyrim, the stores themselves aren't as obviously signposted and may result in you missing that they are there altogether.
Garyn Ienth is technically the general goods merchant in Raven Rock, but his inventory is almost exclusively limited to various food items that he has grown in the ash surrounding the area and is pretty useless if you're looking for the normal items found in a general store, such as potions, Soul Gems, or equipment. However, if you are into cooking in Skyrim, he is easily one of the better merchants around for finding food items, particularly those that only grown on Solstheim.
The somewhat strangely named Retching Netch is the inn found in Raven Rock and the only inn on the entire island. There are multiple short quests that can be started from the Retching Netch and is also where you can find Teldryn Sero, a mercenary for hire with high levels in One-Handed, Destruction, and Conjuration, making him a good all-round fighter for most scenarios.
Glover Mallory, brother of Delvin Mallory who makes an appearance in the Thieves Guild questline, is the local blacksmith in Raven Rock and is found opposite The Retching Netch along the main housing area. Glover is one of the only non-elves that live and work in Raven Rock and spends most of his time sitting at a grindstone, waiting for someone to talk to him. His wares are fairly standard for a blacksmith, though he often has Dragonborn exclusive gear, such as Chitin armor.
Loot
While there isn't much in the way of loot in Raven Rock, there are quite a few plants around the area that only grow on Solstheim, as well as several creatures, like the Netch, that lurk around the waters and outskirts of the area. However, there are a handful of useful items that can be found inside the various houses around Raven Rock, some of which trigger various side quests.
The most notable is a copy of Deathbrand, which will trigger the side quest of the same name that sees you track down each piece of the Deathbrand Armor, which has its best use when equipped on a character that uses dual-wielding melee combat. This book can be found inside The Retching Netch, on a bookshelf in the north-most bedroom.
You can also obtain the Blackguard Armor set by doing a short quest for Glover Mallory, where he sends you to find the improved Bonemold Formula and will give you a key to his backroom when you return with the recipe. After reading this recipe, you will also be able to craft Improved Bonemold Armor, which has a higher armor rating than Dwarven Armor but weighs less.
Raven Rock Mine, a derelict mine on the outskirts of Raven Rock, holds many great items and loot to find inside, including the Bloodskal Blade, the Dragon Priest mask Zahkriisos, and a Word Wall for one of the words of power for Dragon Aspect. There are also several Ebony and Iron Veins that can be mined as well as four Potions of Waterwalking, unique potions that can't be created yourself.
Quests
Raven Rock may be a small town settlement, but there's a lot of quests that can be started here. Glover Mallory will give you the quest Paid In Full to find the Improved Bonemold Recipe, as well as have a letter addressed to Sapphire in Riften where, if it is given to her, she will reward you with an Exquisite Sapphire.
The side quest The Final Descent can also be started, which sends you to Raven Rock Mine to find out what happened to Crescius Caerellius' great grandfather, Gratian. This quest will not only reward you with the Bloodskal Blade, but also force you into a battle with Zahkriisos, a very powerful Dragon Priest with a unique mask the increases all damage dealt by Shock magic.
March of the Dead, a side quest where you are investigating the Ash Spawn and their leader, General Falx Carius, can also be started just outside the walls of Raven Rock. Falx Carius is wielding the Champion's Cudgel, a unique Warhammer that deals Chaos Damage, an enchantment that has a 50% chance to deal either Shock, Fire, or Frost damage on each hit.
Although the Dark Brotherhood doesn't operate on Solstheim, the Morag Tong assassins do, and a quest surrounding their attempt to kill Lleril Morvayn, Served Cold, can be started by talking to Adril Arano. This is the same character that greets you as soon as you disembark from the Northern Maiden, so he and his quest are hard to miss.
There are also many miscellaneous side quests that can be started in Raven Rock, including clearing a temple of Ash Spawn, distributing Sadri's Sujamma, finding a hidden stash of wine in Raven Rock, locating Cindiri's Folio inside the Wreck of the Strident Squall, and retrieving a Nordic Pickaxe for Glover Mallory.
Secrets
Solstheim may be an alien world compared to Skyrim, but there aren't that many hidden aspects to Raven Rock that aren't discovered at some point throughout the main quests or side quests. That being said, Glover Mallory has some intriguing aspects about him that make him stand out among the Dunmer. For one, the lockbox in his house will never reset, meaning it is a good place to dump gear you want to sell or hold onto for later while not having to worry about losing anything.
Through Glover's Letter, it is also revealed that Sapphire is his daughter, who he abandoned shortly after her birth and didn't return to her home until 15 years later, after she had already been kidnapped and sold off. Although Delvin seemed to know the truth behind her parentage, he never told Sapphire and she only discovers the truth if you deliver the letter to her.