间
JLPT HSK 2

jiān, jiàn
Outside: gate 门/門, inside: sun 日
The gate 門 has two wings (with a gap) and the sun shines between.

	简
JLPT HSK 3

jiǎn
Top: bamboo 竹, below: gap/space 间/間 (The sun 日 shines though the gate 门/門 due to a gap.)
(With a fence, it is time-consuming to cut the elements to fit precisely and without gaps). If you build bamboo on a gap (= with spaces in between), you make it very simple.

	涧
JLPT no HSK

jiàn
Left: water 氵, right: between, gap 间 (The sun 日 shines though the gate 门/門 due to a gap.)
The water that flows for a day 日 through a gate 门 (here: gorge) is a: mountain stream.