Ideas for a treasure hunt?

I’d like to do something special for my significant other’s birthday. The basic idea is to have a “treasure hunt” that begins one week before his birthday. I thought I’d create a “message in a bottle” that contains a clue to another location where a small gift and another clue will be waiting. Ending in a romantic getaway on the day of his birthday. Has anyone done something like this or
do you have some great ideas that you can share with me?

Thanks for your help!

I have this all set up, but my SO has been unwell, busy, out of the country every birthday since I came up with it. Here are some of my ideas that you can feel free to use if you like any.

Make a little website with one of the clues.
Write the addy on a piece of paper and put in in an obscure book in the library.
Send them a text message with the book title on their cellphone.
Have the web address have a clue to some landmark near you, a statue or so.
Tape a key to the clue (where it can’t be seen is best) that goes to either a railway station lock box, or a hotel room, or whatever you fancy.

I have more ideas somewhere, I might be back.

My daughter and I video’d clues for my wife to figure out and then find the ‘treasures’ that eventually built up to a nice surprise.

We taped them all at the same time but onto different tapes then hid them throughout the house, in extremely obscure places.

Some took her minutes to find, some took hours to work through the ‘clues’.

You don’t have to keep all of the clues in the house either. You can use the garage, shed, under the wheelbarrow, etc.