You could try kayaking. In that case, of course, you need to pay for the equipment.

in 是介词，表示"在...情况下"或"关于"。 that 是指示代词，指代前面提到的"试试皮划艇"这个建议。 case 的意思是"情况、事例"。 in that case 是一个固定短语，意思是"那样的话"或"既然如此"，用于承接上文提到的情况。