It is some type of junction box. It says Safety Control on the box. There's no door on the box, it's screwed shut. Also, the bell looking thing is plumbed to a 2" pipe and it appears to be some sort of vent. Could it be for an old hot tub that's no longer installed (for bubbles) ?
The other arrow, on the left is a blower for air jets in a spa.
The other, a junction box. Maybe you should turn off the breaker and remove the cover and post another photo so we can see if it's just to connect wires or that is something else in there.
The thing on the left is an air blower. The box on the wall is likely to be an air pressure control switch for the air blower.
The reason for using a pneumatically controlled switch is so that you can activate the blower while in the water without touching an electrical switch.
Probably similar to this:
Allied Innovations Control AS-2-95 No Button 240V 922005-001
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