>nad morzem-at the seaside
correct; moze byc rowniez 'on the sea', np. 'a beautiful town on the Baltic Sea', lub 'by the sea', np. 'we spent the whole evening by the sea'
jechac nad morze - go to the seaside
>nad jeziorem-at the lake
raczej 'on the lake'; lub tez 'by the lake', np. 'there was a couple kissing by the lake'
jechac nad jezioro - go to the lake
>nad rzeką-at the river
raczej 'on the river' lub 'by the river', np. 'my village is located on the river Beaver'; 'we rode our bicycles by the river'
jechac nad rzeke - go to the river
>w górach-in the mountains?
correct; jechac w gory - go (in)to the mountains