GW2. Molten Furnace Fractal Guide
Kill the mobs at the beginning to progress the drill into the tunnel. Once you are in the tunnel, enter the side rooms and kill the mobs there to reveal a blocked vent which you can destroy to open up access further into the tunnel. Repeat this until you get out of the tunnel.
At the end of the tunnel is a large group of charr you must kill. Use line of sight to gather them and AoE them. Pass through the air vents ahead when they are not active and descend the cliff towards the boss room.
The boss is a testing facility where you must survive a series of trials while killing mobs and damaging the thermal core. There are weights that will pound the ground around the four corners and create shock waves. Jump over these. There will also be fire shot on most of the ground space. Tornados will also appear on either side of the room. Hide behind the thermal core to avoid the tornados. As you progress through, more and more of these mechanics will overlap. Once the thermal core is finished, the boss pops up but is a free kill without its devices.