Arnaud, nothing easy here for us Russians:) I can't readily understand досто- part pretty much like you. As a wanna-be fluent speaker of Russian you aren't supposed to be able to deconstruct it further than досто + при-меч-ать-ельн-ость.:-)
This way of word formation isn't productive today both morthologicaly (why did they omit the suffix -й-н- and turned root -о from до-сто-й-н- into connective '-o-'??)
and semantically (if I said достойно-примечательный today, I'd rather interpret it as 'noticeable in a decent manner' than as 'worth of being noticed'. In the latter case I'd use two separate words, not a compound!).
But at some point in history it should be productive, as we have: достоверный, достославный, достопочненный, достопямятный (достопримечательность and достоверный are much used today).
WIktionary proposes Greek ἀξιοθέατος as the sourse. And they well may be right!
Up to 19 century literary Russian experienced heavy influence of Old Church Slavonic (the same way western languages were uder influence of latin).
Old Church Slavonic is the language born from the efforts to translate Greek religious texts into spoken old Bulgarian.
Greek posses a LOT of compounds with ἀξιο-
Among them I see
αξιομνημονευτος - достопямятный
αξιοπιστος - достоверный.