Engine bay Mystery box

[SteatoLegato]

A bit of an embarrassing one, but I can't find the answer online and the box doesn't have any markings on it for easy ID
Back left corner, circled on the pic - what is it and whats' inside? thanks!

 

[smorris_12]

There be dragons! That's why it's screwed down!

(Ok, it's just a waterproof box the engine ECU lives in.)

 

[TriggerFish]

There's also another fuse box in there too (as well as the ECU), so keep that in mind if you ever need to check any fuses.