Aha. Titan does have an underground ocean. Or at least, it *could*
have
one, deep and cold and dark and maybe 15% ammonia.

Well, maybe not so cold after all. The current hypothesis explaining
the persistence of methane in Titan's atmosphere requires that there be
a methane-generating process underground somewhere, and if it's not
biogenic, then the next best candidate process is "serpentinisation
[which] is basically the reaction between water and rocks at 100 to 400
degrees C".
(http://www.theaustralian.news.com.au...E29098,00.html)
If that's what's going on, then Titan's interior must be plenty hot
enough to support a liquid water center.