Almost and Nearly are very similar,but sure they have some differences. ※Almost can be used before negative words,but nearly can't. Eg:Almost+no/none/nobody/nothing/… 1、Almost anyone can do this.(use nearly is wrong) 2、Almost no one came to the party.(use nearly is wrong) PS.Almost and nearly can be used before negative verb. ※Nearly can be modified, but almost can‘t Eg:very/pretty/not/…+nearly 1、It’s not nearly so difficult as you think.(use almost is wrong) 2、The car is pretty nearly new.(use almost is wrong) ※When almost means very similar,we can't use nearly. Eg: 1、I almost wish I’d stayed at home.(use nearly is wrong) 2、Our cat understands everything — he’s almost human.(use nearly is wrong) Approximately is used in writing language.It means something is very accurate and the error can be ignored. So in my opinion,when can’t make mistakes about grammar,all of them are interchangeable.But approximately is much further than almost or nearly.

Almost and nearly are synonyms but approx. has a slightly different meaning in some contexts and is probably less common because it is longer word and tends to be used in the measurement of time or distance.

They are all interchangeable in this context, although to my mind, saying approximately would suggest you know the distance to a fairly accurate degree. As a side note, you wouldn't say 'far' in this context, as kilometres already indicates you are discussing distance.