For example:
* "The mountain range posed a significant obstacle to our journey."
* "Their lack of funding was a major obstacle to their success."
However, other prepositions can be used depending on the context. Some examples include:
* "in": "There were many obstacles in their path."
* "on": "The rocks were an obstacle on the road."
* "for": "This regulation is an obstacle for small businesses."
Ultimately, the best preposition to use will depend on the specific meaning you want to convey.