One of the only places in the world you can see blue flames! ...unfortunately we didn't get to see them because it turned out when we got there that the lava was too high to go down to where you can see them, but the volcano, lake and views were still incredible!
Mount batur is the most popular hike in Bali but if you get the chance to travel a bit further to Java, it's actually an easier hike, and more beautiful to be honest!
If you do see the blue flames, it'll be the trip of a lifetime!
Personally we drove to the port in Gilimanuk, took our bikes on the boat over to Java and then drove to a hotel called Grand Harvest Banyuwangi (nothing special, just a place to sleep for a few hours), and woke up in time to drive to the start of the hike and walk up in time for sunrise (which we missed lol). But you could organise a driver instead of doing what we did.
It took about 30 minutes to drive to the start of the hike and it was cold, so warm clothing was necessary but not after that first drive, entrance and gas masks were very cheap. The hike took about 1.5 hours to reach the crater where the lake is, and you can walk for another 20 mins or so around the ridge. It's also a flat incline walk so it's very manageable, whereas some people find Mount Batur quite rough!