除此以外 is a fixed phrase meaning 'except for this' or 'in addition'. It's used to introduce either an exclusion from a previous statement or an additional point on top of what's been said. Structurally it's 除 ('except') + 此 ('this') + 以外 ('beyond/other than'), and it behaves like a conjunction linking two ideas. In speech and writing it serves both as a contrast marker ('other than that') and an additive marker ('besides that').