Where to go now

[luckyduck]

I spent 4 months in Mexico last year- 3 working in Puerto Vallarta, and 3 weeks traveling. I visited Guadaljara, Mexico City, Oaxaca City, San Cristobel, Palenque (&surrounding area). I am planning on going back to Mexico for a month this summer, and was wondering if anyone had any advice on where else is worth going to, the only idea i have at the moment in Yucatan, but thats a bit vague. So any
ideas would be appreciated! Thanks