NOTE: This will become easy when a release of Cachly that allows bulk adding an offline list to a bookmark list happens. I think it will be soon but Nic can comment. If you need to do this sooner, I've outlined two ways to do it below.
Geocaching.com seems to give minimal support to GPX which is surprising because it is the "standard" interchange medium across devices and platforms. They provide minimal export via PQs and the GPX file button on a cache page. Their "proprietary" exchange mechanism is book mark lists. So given a GPX, you need to navigate this hurdle. My mechanism is as follows:
1) Use urlhttp://jakuje.dta3.com/gpx2gc.html and choose your GPX file. This tools extracts the GC codes. Copy this list to the clipboard.
2) In Project GC, create a new list in the Virtual GPS. This requires a premium membership. The create list dialog has a place to paste the list of GC codes.
3) Create a new empty bookmark list on geocaching.com as they API offers no way to create a list.
4) Click the checkmark box above the top of all the individual check mark lines. This selects all your caches. I'm not 100% certain you need to do this but play it safe.
5) in the Export dropdown, choose Export to bookmark list and select the new empty list you made and click Export. Presto, your list now has the GCs from the GPX.
You can accomplish the same thing using cachetur.no which won't require a PGC premium membership. Register for a free membership. Then do the following:
1) Use urlhttp://jakuje.dta3.com/gpx2gc.html and choose your GPX file. This tools extracts the GC codes. Copy this list to the clipboard.
2) Choose Create New Trip from the Trips menu. Under the Waypoints tab on the create trip screen, is an Add list of GC-codes. Paste your copied list there. Then switch to the Trip Info tab and fill in the mandatory stuff and Save the Trip.
3) Now that the trip is created, from the Download menu, choose Export to bookmark list (note: you may have to create a new list on geocaching.com before this step) Presto, you now have a list from the GPX.
If the purpose of the LIst is to share with others, be aware that cachetur.no has a lot of features you should explore includiing sharing trip planning/execution with travel companions.
