Go straight from here all the way to the end of the walkway for the toilet.
The toilet is all the way at the end of the walkway, going straight from here.
「トイレ」→「Toilet」、もっと丁寧な言い方は「Lavatory, Restroom」といいましょう。
「まっすぐ行く」→「To go straight」
「(歩道の)突き当りの奥」→「The end of (the walkway)」
まとめて言いますと、
「Go straight from here all the way to the end of the walkway for the toilet.」
「The toilet is all the way at the end of the walkway, going straight from here.」
と表現します。