Aliya Laregel-Visiting the Temple on a festival:
The Mitzvah in Temple times: In Temple times, it was a Biblical command for every man to visit the Temple on Yom Tov of the Shalosh Regalim, and bring with them a Karban Olah. This Mitzvah was formally known as the Mitzvah of Reiyah, and its Karban was known as the Karban Reiyah.
The law during exile: The bringing of the Karban is an integral part of the Mitzvah of visitation, of which without it the Mitzvah cannot be fulfilled. Accordingly, during times of exile that we cannot bring a Karban, the Mitzvah is no longer applicable. Some Poskim however rule the Mitzvah is not dependent on the Karban, and hence the Biblical Mitzvah is simply to visit Hashem by the Temple mount area. Nonetheless, since the Mitzvah of visitation is to enter the area of the Azarah, which we cannot enter today due to ritual impurity, therefore it is not possible to fulfill the Mitzvah, even according in their opinion. Some Poskim however rule the Mitzvah is applicable even today. [Some Poskim novelize the Mitzvah can be fulfilled through seeing the floor of the Azara, even if he is not physically there. Accordingly, some meticulous Jews of Jerusalem Jewry are accustomed during the festival to visit a high enough area to be able to see the floor of the Temple mount. Others suggest that even seeing the Kosel suffices for this regard. Other Poskim rule that although the positive command of Aliyah Laregel is not obligatory today, one who does so fulfills a Biblical obligation.] Practically, the Poskim conclude that the Mitzvah of Aliya Liregel is not applicable during exile neither from a Biblical or Rabbinical level, although remains a custom as explained next.
The custom during exile: (Even after the destruction of the Temple, the custom was to gather from all the surrounding cities of Jerusalem and visit the Temple for the festival. This is done even today.) [Practically, it is Mitzvah for every person to strive to fulfill this custom.]
For how many days does the Mitzvah apply: The Biblical Mitzvah of Aliyah Laregel mainly applied on the first day of the festival. Nevertheless, one who did not do so was able to fulfill the Mitzvah for a remaining six days, for a total of seven days. This applies likewise to the festival of Shavuos. If one did not perform the Mitzvah of Aliya Liregel on the first day of Shavuos, he could fulfill it for the next six days. [Accordingly, one who was unable to visit the Western Wall on the first day of Yom Tov, is to do so during one of the next six days. This applies likewise to Shavuos. Those who live near the Temple area, visit it on the first day of Shavuos. Those that live far, visit it between the 7th and 12th day of Sivan.]
What area of Jerusalem is one to visit?
 Devarim 16/16; Rambam Hilchos Chagiga 1/1; Chinuch 489; Semag 360
 Rambam Hilchos Chagiga 1/1; Chinuch 489; Semag 360; Ridbaz on Yerushalmi Chagiga 1/1; Turei Even Chagiga 2a that so is opinion of Bavli; See Minchas Chinuch 489-490; Noda Beyehuda Tinayna 94; Yearos Devash 1/12
 Turei Even Chagiga 2a that so is opinion of Yerushalmi; Yireim 425; 403 “When one comes to see Hashem, he is to bring charity or a Karban”
 See Chagiga 7a; Rambam Chagiga 1/1
 Yachel Yisrael 1/14
 Tashbatz 3/201; Chasam Sofer Hesped after Parshas Emor “It is a Mitzvah to visit Lalos Liregel even today”; Chasam Sofer Y.D. 233; However see Chasam Sofer ibid 234 “In today’s time there is no obligation”; Yechaveh Daas 1/25 “Certainly there is a Mitzvah also today”, although see Yechaveh Daas 2/10 who writes it does not apply today
 It is unclear if his intent is Biblical or Rabbinical
 Rav Shlezinger, student of Chasam Sofer, in Shut Rav Akiva Yosef 160, brought in Piskeiy Teshuvos 529 footnote 51
 Har Hakadosh p. 277; Custom of Rav SZ”A
 See Siach Yitzchak 2/142
 Mishneh Halachos 12/489; Piskeiy Teshuvos 529/13; Perhaps this is the intent of Chasam Sofer and Yechaveh Daas ibid; See also Or Letziyon 3/24-12
 Implication of Admur 117/1 in parentheses; Levush 117/1; Ran Taanis 2a; Ridbaz on Yerushalmi Chagiga 1/1; Minchas Chinuch 489-490; Noda Beyehuda Tinayna 94; Yearos Devash 1/12
Igros Moshe Y.D. 3/122
 Admur 117/1 in parentheses; Levush 117/1; Ran Taanis 2a; Midrash Shir Hashirim 4/2 “Just as a dove returns to visit its destroyed nest, so too the Jewish people visit the Temple during Shalosh Regalim even after the destruction; Sefer Chassidim 630 “Rav Haiy Gaon would travel to Yerushalayim from Bavel to be there for Sukkos”; Kaftor Vaferach 6 “We are accustomed together with the lands of Syria, and Egypt to visit the Yerushalyim by the Moadim”; Maharit 1/134; Maharitz Chayos on Nedarim 23a; Tashbatz 3/201; Maharalbach; Yaavetz 1/87; Avos Harosh 1/117; Sdei Chemed Mareches Eretz Yisrael 1; Igros Moshe Y.D. 3/122; Piskeiy Teshuvos 529/13
 Chasam Sofer Hesped after Parshas Emor “It is a Mitzvah to visit Lalos Liregel even today”; Chasam Sofer Y.D. 233; Sdei Chemed ibid; Yechaveh Daas 1/25 “Certainly there is a Mitzvah also today”; Or Letziyon 3/24-12
 Rambam Hilchos Chagiga 1/4
 Rambam Hilchos Chagiga 1/7
 Piskeiy Teshuvos 529/13 footnote 49