Actually, I'd like to know how I should say, for example, "Irei para São Paulo no final de semana", "Meus pais costumam me visitar nos finais de semana", "Terei que trabalhar neste final de semana", etc.

And I have another question about prepositions... I've read on internet these sentences (www.englishpage.com):

- Fred loves to go camping in the desert, but Kyle prefers to camp in the mountains.

- While they were hiking on Ridgeback Mountain, Laurelle and Frank saw a bear in the woods.

Why in first sentence is written "IN the mountain", and in the second "ON Ridgeback Mountain"?

Thank you very much!