Blizzard's approach to the MOBA in Heroes of the Storm has always put a lot of emphasis on the board mechanics. Yes, all the battlegrounds are built around knocking down walls, towers, fortresses keeps and cores, but the maps' various special objectives have always been powerful enough to make you deviate from your standard forward push.
Notably, the Haunted Mine map has been indefinitely removed, as they felt that it was structurally flawed (I always liked it, but it's true that the grave golems - spawning even if your team didn't get a single skull and also starting exactly where it fell - were perhaps overpowered and game-breaking.)
However, in its place we've gotten Towers of Doom, which is by far the most convoluted battleground in the game. It's fun, mind you, and holy crap do I love the aesthetic of it, but it's very unconventional compared to any other map in the game.
Actually, before we get into mechanics, I just want to sing the praises of the aesthetics. It seems to take place in a kind of haunted urban location. One team plays for the Gravekeeper - the announcer in the now-defunct Haunted Mines map, and the other plays for the Raven King, who is the announcer for the Raven Court map. Combined with several alternate costumes for several characters (which are generally justified as being alternate-universe versions of those characters,) and there's kind of an original setting (or a few) slowly being constructed within Heroes of the Storm. To top it off, the "Boss" mercenary on the map is the Headless Horseman, and the whole place has a very spooky-fun feel to it. Man, I'm in love.
The big twist here is that you don't actually get to attack the enemy core directly. Both cores are surrounded by a thick wall that is covered with a million cannons that will make short work (though not instant) of anyone who steps over the clear line marking territory.
Instead, there are a total of six bell towers (three on each side) that, along with your core, will help you take down the enemy core.
Destroy an enemy bell tower, and one of yours will rise in its place. This means that the opponent will essentially have to re-capture their towers if they want them back. Destroying the tower also destroys related structures, so if you really focus down the tower, you might skip dealing with the nearby turret.
However, you'll have to fight pretty hard to hold on to captured towers, as the enemy will spawn rather close to the ones that were originally theirs.
Why capture the towers? Well, that's the second piece of the puzzle.
Around the map are, I believe, five Altars. Periodically, two of these will activate. If you can capture an altar, this will cause each bell tower you control, as well as your core, to launch projectiles at the enemy core. To simplify things, the core only has I believe 40 health to begin with, and each projectile does one damage.
So while you'll certainly get an advantage (potentially dealing 7 damage to the enemy's core if you control the whole map,) if you capture lots of bell towers, you'll definitely want to prioritize getting those Altars, as not only will they be used up after one use (though they will eventually be reactivated,) but your enemy will still be able to do at least some damage to your core even if you control everything else on the map.
There are a few mercenaries to be found around the map. Most of them are pumpkin soldiers, who I believe toss bombs at structures and can help you capture bell towers. Defeating the Headless Horseman will cause him to toss 4 pumpkin bombs at the enemy core.
Periodically, the dark lord that you're serving will open a tunnel from your core to the center of the map to make getting back into the fight easier.
While it's never wise to ignore map mechanics in Heroes of the Storm, in Towers of Doom you literally can't win unless you make use of them. The fact that you're really capturing, rather than simply destroying the various strongholds means that playing defensively becomes a far more important part of the strategy. Basically, a bell tower saved is a bell tower earned.