Complex sentence: Thus most of the platform is high, and is accessible (at least upwards) by escalator, but there is a cutout section taking the level down to one foot above ground, to board the trams.
Split into simpler sentences: Thus most of the platform is high, and is connected to the street (at least in the upward direction) by escalator. But there is a cutout section taking the level down to one foot above ground, to board the trams.