+I made my way to the ex-Convento de San Francisco. In mistake, I enter the museum looking for "La Conquistadora," which in reality lies in a chapel next door. The museum closes during siesta time so go in the morning or the afternoon. After waiting for a few hours for it to reenter, I got a peak of "la Conquistadora," which is the virgin carried by Hernan Cortez in his armor and his chest/breast. I also took a peak on the basin used to baptize the four Tlaxcalteca lord at the time of the alliance. Before you go, make sure you look up at the beautiful roof. It is covered by beautiful Moorish style woodwork (still in its original form). If you liked the roof, then check out the roof of the Catedral de San Cristobal de las Casas in Chiapas since it shares a similar craftsmanship.
I made it to the Plaza Constitucion de Tlaxcala. One can admire the Capilla Real de los Indias (now the Palacio de Justicia) and the Palacio de Gobierno. Inside this last place, you can find amazing murals depicting Tlaxcala's history. History says that the 4 chiefdoms of Tlaxcala allied with Cortez and in by doing so guaranteed his victory and eventual conquest of the Aztec empire.
There are several buses going to Puebla so don't wory as far as transportation goes.
There are several collectivos that go near the ruins of Cacaxtla and Xochitencatl
If you have the time, I would definitly reccommend a visit to both Cacaxtla & Xochitencatl. Both sites are near each other. Cacaxtla has dozen of colorful murals, a rarity in Meso-American archeological sites. Read more about this two archeological sights at my Estado de Tlaxcala page.