Railay Beach is beautiful and less packed than the other beaches in Southern Thailand. And, between Railay and Tonsai, there is world class climbing. I loved my stay there (lots of photos of it on my instagram and likely in future posts).
But - I remember doing lots of searching on the interwebs on this particular stretch since there seemed to be a lot of options.
1) Take a bus - there are overnight buses that you can take. My back and knees are much too old for that in my 30s, so I nixed this. Plus, with the costs down there so much lower, double the price for flying was totally worthwhile (about 75 USD round trip).
2) There's not a train option.
3) Fly! Which is what the rest of this post will be about. But, it's not a direct flight like it is to spots like Phucket.
Railay Beach from Bangkok via Air
A quick google search lets you know that AirAsia is the least expensive option - so I went with that (friends and the interwebs told me that this was totally safe and okay). AirAsia doesn't depart from BKK (the airport you likely flew into Bangkok if coming from the US), but from DMK which is about half an hour north of the city.
You'll be flying from DMK to Krabi (KBV):
1) Uber super early in the morning from my airbnb - which is easier than hailing a cab from Sukhumvit where I was staying, at least at 4:30am. There's no direct train to DMK (Don Muang), so taxi or uber is the best way to go. It's about 350 baht.
2) Airport check in is organized by flight, not by airline. Also, not all cab drivers will know where domestic is and where international is (unlike in other cities). The usual airport security applies (no liquids, electronics need to be taken out, etc).
3) Typically (for AirAsia at least), there's a shuttle that takes you from the gate to the plane - when they're ready for boarding, they'll start having everyone pile into the shuttle.
4) Once you get to Krabi, grab your things and head toward the exit. It's a small airport, so not a lot of confusion there. The easiest next step is to get a taxi/car to one of two ports: Ao Nang or Ao Nam Mao. The tax costs about 700 baht from what I recall (about 20 USD, so be sure to have enough cash). There should be a taxi stand that is semi-established feeling that will grab you a car/taxi.
Ao Nang boats will take you to West Railay beach where there is a WET landing. It's also the beachy side of the peninsula (it's not an island) where the bigger resorts are. So, be prepared with flip flops and such. Ao Nam Mao will take you to the East Railay pier.
5) It sounds like both piers function similarly - I went to Ao Nam Mao - and you get a ticket to enter a queue to wait for a long tail boat to fill up. I suggest you time your flight so that you're there during normal hours (not evening) so that it takes no longer than 30 minutes or so of waiting. They pretend like there are times that the boats leave, but my experience was similar to others - they just wait for it to fill up. This was inexpensive. The driver and boat sales person might ask you to purchase a return home - it'll be over priced. I suggest you get a return home "tour" from the tour stand in front of the Avatar Hotel on East Railay. It was about half the price quoted (good thing I emailed them ahead of time!).
6) The boat ride is wet or can be. And if it happens to rain, you could get even wetter. Not a bad idea to have one of those plastic rain thingies with you just in case! From the East Railay Pier, it was super easy to find my hotel, Avatar. Just walk north (or to the right when coming from the pier) - most other hotels are that direction as well.
The way back...
Is way easier! But, with a few quirks worth mentioning. Purchase a "tour" from the tour stand in front of Avatar Hotel (or from other tour stands, there are plenty all over the small Railay area). It'll include your long tail boat and car voucher. If leaving from the East, you find someone at the pier and show them your purchase and you'll get into your "tour group." Depending on time of day (low and high tide) you may enter Ao Nam Mao at a different pier than the one you left from (which is what happened to me). You show your car voucher to random cars and see if anyone takes that voucher - a bit odd since it's not like a particular car is tagged to you. It sounds like the "tour" just makes sure there are enough cars waiting for you at approximately the right time at the pier for pick up to the airport.
Quit my non-profit career in a fit of YOLO rage. Blessed enough to go from wanderlust to wanderslut. Collecting cities & countries, not men.