It used to be a quiet medium-sized town, but in recent years big developments have sprung up like mushrooms.

它曾是一座安静的中型城镇，但近年来，大型开发项目如雨后春笋般涌现。

To spring up like mushrooms, that means to grow very quickly and that's a common idiom to talk about buildings.

to spring up like mushroom，意思是长得非常快，这是用来描述建筑的常用习语。

Little poufs and tables of knickknacks spring up like mushrooms, and the walls are lined with Stratocasters and Flying Vs, violins, an assortment of harps, one stout cello propped up in the corner.

小坐垫和摆满小玩意的桌子像蘑菇一样涌现，墙壁上排列着 Stratocaster 和 Flying Vs、小提琴、各种竖琴，角落里支着一把粗壮的大提琴。