僕はまだ三途の川を見たくはない。

。

I don't want to see the Sanzu River just yet.

Literal

I [topic-は] still Sanzu-River [object-を] see-want [emphasis-は] not.

三途の川 (さんずのかわ, 'the Sanzu River') is the river of the dead in Buddhist cosmology — the Japanese equivalent of the River Styx. Saying 'I don't want to see it yet' is a colorful way of saying 'I'm not ready to die.' まだ ('yet') + ~たくはない ('don't want to,' with は for emphasis).