for the tower and the spider: it's a feature : having a tower in the cultura border give the civ it's line of sight : as if you had a unit on the tower.
(in the same way, when the culture border is on a peak you gsee 3 tiles away, and if there is a hill or a forest just 1 tile out of your border, you don't see past it (you see 1 tile away instead of 2))
IIRC, in your photo wuth the spider you had in your cultural border :
a peak that allow you to see tiles behind the forest the spider is on (from the right to the left)
a tower that see invisible units in a 3 tiles square... see the spider.
(in the same way, when the culture border is on a peak you gsee 3 tiles away, and if there is a hill or a forest just 1 tile out of your border, you don't see past it (you see 1 tile away instead of 2))
IIRC, in your photo wuth the spider you had in your cultural border :
a peak that allow you to see tiles behind the forest the spider is on (from the right to the left)
a tower that see invisible units in a 3 tiles square... see the spider.