Guatemala is a cheap and easy tourist destination: practically every hostel is connected with a travel agency, which offers transportation to all local sites and well beyond at very reasonable rates. You can also book guides through these agencies. Although Guatemala has a high crime rate and tourists have frequently reported muggings, it is perfectly safe if you hire tour guides, stay with a group, and ask the staff at your hostel whether there are any parts of the town that you should avoid. Guides typically cost $5-15 per tour, and they are very worthwhile – both for their knowledge and the security they provide.
The most famous site in Guatemala is Tikal, which features the magnificent ruins of an ancient Mayan city, including excavated, step-pyramid temples. There is also an interesting array of wildlife, including spider monkeys, howler monkeys, tarantulas, and a variety of trees. I recommend staying in Flores, which is an island town on stunning Lake Peten Itza that is approximately 45 minutes from Tikal. Our $15-per-person tour included a van ride from our hostel in Flores to Tikal; admission into the park; an English-speaking tour guide; and transportation back to our hostel. I recommend going in the morning – particularly during the summer, because it gets uncomfortably hot in the afternoon. You probably need 4-6 hours in Tikal.