Do you want to be in a "public" setting or rather alone? While the restaurant idea is great, she'll have to constrain herself if she wants to cry etc etc. It cannot be as intimate as when it's just the two of you...
I asked my wife when it was just the two of us and that worked perfect for us. Do it in a location your gf will feel comfortable..
You guys don't stay together and aren't going away, so this one may be tough, but here's an idea (Not how I did it, just an idea):
Spend the day at spa with her and tell her how you love her etc etc. Chat about how you met and throughout the day, without making it glaringly obvious, remind her of some of the great times you've shared.
Then after you've had this fun-filled trip and you're heading home, wait for her to get into the shower or something that will take up some time. (If you think she'd like to look good on her engagement-moment pictures then do it after a dinner or something)
1 - Put a small gift (teddybear or something) outside the door with the oldest picture you can find of you two. Put the picture facing downwards and write something on the back of it about where and how you met, also give a clue as to where to find the next picture, or just create a trail with rose-petals leading her to the next picture.
2 - Get a picture where the two of you look in love (kissing, holding hands, hugging, anything). On the back, explain to her what you felt when you fell in love with her for the first time, describe something like the way her hair smelled or how your stomach had butterflies for a week. Again give a clue to the next picture's location or make a petal-trail
3 - Get a picture of something that reminds her of a tough time you've been through together, explain how you won't let anything come between you. If the tough thing you've been through will spoil the mood, take a picture of your dirty socks lying on the ground and write something about her being the reason you want to become a better person and how you're trying not to let it lie around any more or something. Again on to the next picture/clue
4 - Anniversary picture + memory or something
Continue this walk down memory lane, you can have anything you like in there, you can possibly put something like a picture of two really old people holding hands or something and on the back write down how long you've know each other (use roughly the time you'll ask her to marry you) and write it out in different ways..
5 - End with the last picture right in front of a closed door, on the back of the picture tell her to knock three times, wait 10 seconds and then enter.
By now you have her thinking about all the great times with you, you told her how you won't let things come between you, etc. The great thing about this, is that once she enters the door, you only have to say one sentence. (I feel the proposals where the guy says all the stuff that's supposed to be on the pictures aren't as powerful as just asking her to be your wife when she sees you..)
You wait in there, you can softly play her favorite song in the background once she knocks, you can change into a suit, you can fill the room with 200 candles, anything you like, but when she opens that door, make sure you're on the other side on one knee.
Simply say: "I love you, will you be my wife" or something short and powerful like that, she'll remember the one sentence forever..
Nothing really matters after this, but you can have a dinner ready by candlelight if you think you'll have an appetite or champagne or whatever - personalize it.
She ends up with:
* An intimate moment
* A gift to remember the moment by (As if the ring isn't enough..?

)
* The actual pictures to keep in an album or something
* Only one sentence to remember when she thinks back at the moment, even though you've said so much more on the pictures too
I'd also have a camera ready and set up with a timer so you can take pictures. If you really feel like it, you can even record a video of the whole thing.
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Point being: Make it personal, customize it to your relationship and focus on your love you share.