I think it's better for us to sleep in tents because it'll be more adventurous than staying in rooms.

adventurous 是形容词，由名词 adventure（冒险）加上形容词后缀 -ous 构成，表示"喜欢冒险的"或"充满冒险精神的"。在这里形容睡帐篷比住房间更有刺激感和冒险性。