Berachos, Chapter 4, Mishnah 6. This mishnah is essentially similar to the previous one, and deals with someone who wishes to daven Shemoneh Esrei while he is in a place where he cannot control the direction in which he stands.
The words of the Mishnah:
"HaYosheiv bisfinah" - one who is sitting in a boat.
"O b'karon" - or in a wagon.
"O ba'asdah" - or on a raft.
"Yechavein es libo k'neged Beis Kodshei HaKodashim" - he should direct his heart toward the Holy of Holies.
Since he cannot get off the boat, the wagon or the raft in order to daven, and he also has no control over the direction of travel, it is upon him to direct his heart - that is, to picture himself in his mind as standing facing the Holy of Holies.
In summary: In this mishnah we learned that one who is traveling in a boat, in a wagon or on a raft, and cannot control the direction in which he stands, fulfills the obligation to face the Holy of Holies through the intent of his heart and mind.