It depends on the way they re presented. Fantasy often calls on myth and existing or putative legends. Space travel is a reality, but at present we can t hope to go far enough in a human life-time to reach another habitable planet. Other dimensions can occur in either. Well, another planet is a place to which you might travel if you had a spaceship that was fast enough.
Fantasy often deals with the clash of good and evil, or of power and the lack of it.
A very common theme is sci fi is the return of medieval ways and attitudes. This often happens after a cataclysmic clash during which technology destroyed a good deal of the world and its civilisation. In fantasy the focus is more likely to be on the ownership of magical power rather than technology. A character who calls up demons will be as feared in fantasy as a scientist who holds the key to an epidemic or bomb will be feared in science fiction. The result is probably best referred to as science fantasy.