I'm studying German on my own and I would like some help with this sentence I read in my textbook:
Deshalb möchte er im Urlaub möglichst viel an der frischen Luft sein, ohne sich zu sehr anstrengen zu müssen.
I get what it means, but there are two things I don't understand:
Isn't "ohne" just a preposition, shouldn't it be "ohne dass" in this case?
Why is there a "zu" in front of "müssen"? I thought modal verbs didn't require a "zu" to connect with the main verb.
Would it also be correct to say "... anstrengen müssen" and would it mean the same?