Open
A gate with a lantern is open for you. That's convenient, since it's pretty dark out and you might not have seen the open gate without the lantern's help.
Imagine being a traveler, walking around the outside of a huge walled city. You really need to get inside but all of the gates are closed. Finally, you see a single, bright lantern marking the open gate! What a relief.
かい
あ, ひら
None
This open gate is in the water though, so you'll need a kayak (かい) to get in. Luckily, you've been carrying your kayak with you just in case.
Imagine kayaking in the dark toward an open gate. Finally, you've made it!