At the back we can get a good overall look at some features you'll not find on regular cases. There are meshes everywhere and three holes for tubing are located at the top as well. Below them you'll notice a 120mm AF120L exhaust fan that comes factory installed. You'll notice that the Obsidian 900D has 5 expansion slots allowing you to go for two-way on your Multi-GPU preference with SLI / CrossfireX configurations.
At the bottom we see space for one power supply, there's plenty of space for even a powerful kilowatt PSUs.
Back to the top side again, the top side cover is a mesh that is all about ventilation alright. The Obsidian Series 350D is supplied with 2 fans as standard, one 140mm intake fan and one 120mm exhaust fan. A total of 5 fans can be installed. At the top side there is space to include up to a 280mm radiator at the roof of the case, and a 120mm radiator in the rear exhaust fan mounting area. All-in-one-coolers such as the Hydro Series H55, H60, H80i, H100i, H90 and H110 are supported. When mounting a full length radiator on the roof of the case, the upper 5.25 inch optical drive bay will be partially blocked by the radiator though.
You'll notice that in the top middle an extended plastic bar eh? That is your power button with HDD LED activity, below it a reset button. Then to the left 3.5mm headphone and microphone jacks, in blue two USB 3.0 ports.