When he gets up to pray if he was standing outside the Land of Israel, he should return his face toward the Land of Israel and focus also on Jerusalem and to the Temple and to the Holy of Holies. If he was standing in Jerusalem he should return his face to the Temple and focus also to the Holy of Holies. If he was standing behind the (Ark) he should return his face to the (Ark)....
If one prays [facing] one of the other directions, one should turn one's face to the direction of the land of Israel if one is in the Diaspora; and to Jerusalem if one is in the land of Israel; and to the Temple if one is in Jerusalem. Gloss: And we who turn our faces to the east, it is because we dwell to the west of the land of Israel, and so our faces are towards the land of Israel (Tur, Orach Chaim 94:1 and Sefer Mitzvot Gadol). We do not make the place of the ark [in our synagogue] and the direction of prayer exactly opposite the sunrise because that is the way of the heretics; rather we direct [ourselves] opposite [the direction of the sun] in the middle of the day (Hagahot Alfasi haChadashim) And one who wants to uphold their saying (i.e. that of the Sages): "The one who wants to gain wealth turns northward or to gain wisdom turns southward", nevertheless should turn one's face towards the east
One who is not able to determine the [compass] directions, [should] direct one's heart to one's Father who is in Heaven.
If one was riding on a donkey, there no need to get down and to pray even if one has someone to hold on to his donkey, rather, one [should] pray while he is going. And so too, if one was on boat or on a wagon - if he is able to stand, he [should] stand, if not, he [should] sit in his place and pray. Or if one was walking by foot, he [may] pray while he is going, even if he is not facing towards Jerusalem, even if he is not in a dangerous place, because if he would stand and pray, the delay in his travels would be difficult in his eyes, and he would become anxious and would not be able to focus. And all [this] is according to the route and according to the place and according to one's fear and peace of mind. And there are those who are strict to stand during Avot [i.e. the first blessing of the Amidah]. And it is appropriate to heed them if one is not in a dangerous place.
If one is sitting on a boat or on a wagon: if he is able to stand up at the place [in the Amidah prayer] of bowing, [then] he [should] stand so that he is bowing while standing and [while taking the] 3 steps [back at the beginning and end of the prayer]. Rem"a: Even though one is sitting for the entire prayer, nevertheless, if it possible for him to stand, he [should] stand in order to fulfill [his obligation to] bow and take the [3] steps properly (Beit Yosef in the name of S"Ch). And if it is not possible for him, for example when he is riding on an animal, he [should] guide the animal to take 3 steps behind it, and it is counted for him as if he is taking steps himself (Hagahot Alfasi haChadashim, end of chapter "The Morning Prayer"
One who is sick [may] pray even lying down on one's side, as long as he is able to concentrate (And if it is not possible from him to pray, nevertheless, one should meditate in one's heart, as it says "Ponder [it] on your bed" [(Psalms 4:5)] (Beit Yosef in the name of Orchot Chaim and Pesikta).
One who has [dangerous] non-Jews on either side of him and fears that perhaps they will interrupt one's prayer [i.e. Amidah] or will cause a loss of one's merchandise: one may sit in one's place and pray since one's mind is not settled regarding it. And even though one needs to take three steps [back] at the end of the prayer, [nevertheless, here] one [just] sits and prays and bows.
One should be careful to not support oneself on a pillar or on one's friend at the time of prayer.
One who must pray sitting, when he is able to he must return and pray standing. And he does not need to add anything in it. Rem"a: And one who is traveling and is near a hotel, if he can remove himself from the road in a place where travelers will not interrupt him, he should remove himself. And he should not pray in a hotel of idol-worshipers so that the residents do not confuse him. But if it is impossible for him to remove himself from the road in a place that they will not interrupt him, he should pray in a hotel in any corner. (Terumas Hadeshen)