If you live near the sea, arrange a romantic travel for your beloved! Hire a cutter/yacht and drive away your girlfriend far into the sea! Beforehand prepare dinner and products for the next day, think about good relaxing music, candles and aroma oil!
Would be super if you hire the cutter/yacht for a weekend, so in the daytime you could swim, bask in the sun, mesmerize before a fascinating view of the sea. At night the atmosphere would be magic, you would be able to spend wild, passionate nights where there is nobody around, so enjoying by each other you could moan very loudly, if you would wish...
By the way if you made up your mind to make proposal to your girlfriend, it's the best time to fulfil it!
To my mind such trip would be marvellous and memorable for the life long!