Also like others said, you can find cave spider spawner easily in a Mineshaft (like picture # 2 of Jim's answer). They always have many cobwebs around, and it's not rare to see 2 spawners near each other.

How many spawners are in a mineshaft?

5½ chest Minecarts (for comparison - about 1.5 gold apples per complex) a median of 5 chests, with ~80% of the Mineshafts having 3-9 chests. about 3 spawners.

What are spawners in mineshafts?

Abandoned Mineshafts are underground structures in Minecraft that spawn in random spots in a Minecraft world. They are dark wooden passages that long-ago miners once wandered searching for treasure. Alas, now they are a darkened and deadly maze, with Cobwebs and Cave Spider spawners at many turns.