21. These features were the last major natural obstacles that had to be crossed prior to reaching Beirut. 22. They see natural obstacles as a challenge and get very creative on how they challenge that obstacle. 23. In some maritime environments such a defence is given by natural obstacles , such as the Arctic ice shelf. 24. The challenge in the game comes almost completely in the form of natural obstacles in the cider factory. 25. Marshlands, other natural obstacles , and barricades made of stone, earth or timber provided defense at the kingdom's borders. 26. Because of its u-shape, the eastern side of the citadel was more vulnerable due to less natural obstacles . 27. It is crossed by three large rivers, but an international system of ferries helps cross these natural obstacles . 28. The marshland of the River Ribble and the Savick Brook were natural obstacles preventing easy access north-west of Preston. 29. A number of major roads link Jordan and Syria in this region, crossing undulating terrain with no natural obstacles . 30. It is a natural obstacle that separates the Shenandoah Valley and Cumberland Valley from the eastern part of Maryland.
