UK, Australian, New Zealand, Canadian, US and South African passport holders travelling to Nicaragua for touristic purposes do not require a visa for stays up to 90 days. If you are a passport holder of another nationality, check Project Visa for more information on visa requirements for Nicaragua.
Guatemala, Honduras and Nicaragua are part of the Central America Border Control Agreement (CA-4). Under the terms of this agreement, tourists can travel within any of the CA-4 countries (which also includes El Salvador) for a period of up to 90 days, without completing entry and exit formalities at border immigration checkpoints. This period begins at the first point of entry in to any of the CA-4 countries. Fines are applied for travellers who exceed this 90-day limit, although a request for a 30-day extension can be made before the 90 days limit expires.