Option B: An 'excursion' is 'a short journey or trip, made by a group of people'.
This word means the same as the given phrase and can substitute for it. Hence option B is correct.
Option A: A 'hike' is 'a long walk, generally across the countryside'.
Option C: A 'picnic' is 'a packed meal eaten outdoors, especially during an outing'.
Option D: A 'stroll' is 'a short leisurely walk'.
These words do not mean the same as the given phrase.
Hence they cannot substitute for it and options A, C and D are wrong.