To gain access to the interior, simply remove the thumb screws holding the panels in place. As with most cases these days, there is a metals shroud and very little else inside the case. This gives you as much space as possible for large components or liquid-cooling elements. Looking at the opposite side, you can clearly see the large opening for the CPU cooler. There are two lines of cable-tie hooks to the left of that, right next to which you will find rubber grommet openings for cable management. Underneath the shroud, you will find the PSU bay and two 3.5" drive trays, which may also be used for 2.5" drives instead.
A small PCB enables the RGB functionality. You may connect it to your motherboard to control the color via software in a synchronized fashion or use the button in the top of the case. Thanks to the standard 4-pin connector, it is easily expanded to suit your requirements. There is around 22 mm worth of space between the motherboard tray and side panel, which should be enough for most scenarios.
You will find a single 2.5" tray underneath the large opening, but there are two additional placement opportunities towards the front of the chassis. Those mounting holes are extruded towards the backside of the motherboard tray, which seems to suggest that you place the drives on this side, hidden away from view. This brings the total number of drive trays to five, which is probably enough for the vast majority of users.
The metal shroud is completely solid with the exception of a hole at the front of the Enso for large radiators of up to 360 mm in size there. Better use of the shroud's surface area would have been nice to, for example, allow for additional 2.5" drives to be placed there. In the front, you will find another 120 mm fan set to pull air into the chassis. As you can see, you will need to install them directly to the front of the chassis, which will have you pry off the front cover to do so.
The seven expansion slots in the rear, above the PSU bay, are covered by metal mesh pieces that may be detached by removing the screws that hold them in place. Above that is the white-bladed 120 mm fan. It comes embedded with RGB LEDs as well, which sync up with the rest of the enclosure's lighting elements. That said, while they are RGB, the cooling unit does not go as far as to offer addressable RGB LEDs, which means that the whole fan will light up in just a color of your choice.
Looking at the ceiling, you will be able to add two 120 mm fans or a 240 mm radiator here. As the mounting hole is centered, you need to make sure that any such cooling unit does not interfere with your motherboard's larger components.
All the cables within the chassis are pretty standard, so you should have no issues connecting things to the board or front of the case.