Are titan's other weakness the underground?


They do seem to become less active at night or if deprived of sunlight, and so
it may be possible they draw their primary source of energy from the sun.
[Annie refused to go
underground.](https://anime.stackexchange.com/questions/13880/how-would-
annies-going-underground-prove-anything) There also seems to be types of [wall
titans](http://shingekinokyojin.wikia.com/wiki/Wall_Titan).

It seems to me that titans are scared of underground and need of sunlight make
them weak to underground. Is this true and if so why doesn't the humans try to
colonize underground?




There is no evidence to suggest that being underground/confined spaces can
actually be a weakness for Titans. However there isn't any evidence supporting
the contrary as well.

A definite **strategic disadvantage** of underground transformation is obvious
(due to the restricted space for movement and the lack of visibility).

However in the corresponding chapter, you would do well to **notice** that the
Titan smashes the tunnel from outside, all too easily. So underground
colonization is a definite **NO**.

There is also no hard evidence on whether sunlight is a primary source of
power for Titans. If that were the case, then Annie's transformation in the
forest would have degenerated (no/minimal sunlight there).

Also (as suggested by
[@mirroroftruth](https://anime.stackexchange.com/a/18373/11643)), the use of
forests is mainly because of the better 3D maneuver environment. However from
my perception, undergrounds are just as _bad_ an environment for 3D maneuvers,
as they **may be** for Titans.

