The Rio San Juan Region is a region in Nicaragua which borders in the south to Plains of the North, Costa Rica
This is largely a rural area, so the term "cities" is something of a stretch. Juigalpa, Boaco and to a lesser degree San Carlos are the only places with the size and services you would commonly associate with a city.
This region has historically been one of the least developed regions of Nicaragua, but in the early 2010s this seemed to change with the construction of a paved highway from San Carlos to Managua slashing travel times and investment making the area attractive to backpackers. However, due to the crisis, the (seemingly permanent) cancellation of the Ometepe-San Carlos ship and a reduction in tourism, the once projected growth seems to be gone and the heyday over. The river, which was considered more than once as a possible route for an inter-oceanic canal linking the Pacific and Atlantic, belongs entirely to Nicaragua, although its right (or southern) bank is Costa Rica beginning a bit downriver from El Castillo all the way to San Juan del Norte. This has in the past sometimes caused frictions between the two countries.
Before the transcontinental railroad was built in the USA, taking a ship down to San Juan del Norte (also known as Greytown) and then a boat through the Rio San Juan up to Lake Nicaragua and crossing the narrow strip of land in the (now) Rivas-departamento was one of the fastest and most practical ways to get from New York to San Francisco. Several notable figures of 19th-century America traveled on this path including Mark Twain, who wrote about the trip in one of his books. This historic route is today known as Ruta del Tránsito and you can still travel on the trail of these first outside travelers to the area. However the boat you will use are powered by internal combustion rather than steam and you would have to go out of your way to go a significant distance by horse drawn carriage.
English is not not prevalent in the Rio San Juan area, as few people have been to university or lived in Miami at some point in their lives. People from Managua and other big cities like to make fun of the supposed hillbilly accent of the people in this part of the country, however there is hardly a noticeable difference to the untrained ear.
Bus from Managua to San Carlos (6 hours, C$150 (córdobas); via Juigalpa).
Twice weekly flights from Managua to San Carlos (US$120 round-trip). Some of them via Ometepe - at least according to official schedules of La Costeña but reportedly scheduled flights to/from San Carlos were not operating in either 2018 or 2019.
Flights from Managua to San Juan del Norte via San Carlos (IATA: NCR)
For all domestic flights check with the website of the only domestic airline - if you can't book it on the website, try to contact their desk at Managua airport and be prepared for the flights not going if they're not bookable online.
Boat from Bluefields to San Juan del Norte (inquire in advance as the schedule keeps changing)
Most of the trips are done on little boats on the Rio San Juan or Lake of Nicaragua.
From San Carlos there are regular public boats downriver every day to El Castillo, stopping at various points on the way, notably Sabalos. If you wish to go beyond El Castillo you'll need to go on occasional public boats that go all the way to the end of the river at San Juan del Norte. It takes 3 hours for most public boats to travel between El Castillo and San Carlos; a faster boat leaves once daily (usually early in the morning) and takes only half as long.
Apart from the San Carlos Juigalpa carretera there are no roads to speak of in this area of Nicaragua; all significant transport between San Carlos and San Juan del Norte is by boat or occasionally plane. The area just beyond El Castillo downriver to San Juan del Norte (San Juan de Nicaragua) is part of the Indio Maiz national park.
To get to the Solentiname islands your best bet is to take a boat from San Carlos. The boats usually leave and arrive from the malecon; for more, see the city article.
A kayak or canoe trip up the Sabalos river, from 1 hour to 3 or 4 hours depending how far or deep you want to get, you can combine the trip with a visit to a cacao plantation, and then come back down stream in the Rio San Juan. You could also arrange for a longer trip all the way down stream to El Castillo is about another 2 hours. For the most adventurous there is the possibility to canoe o kayak all the way to San Juan del Norte, a 4- or 5-day trip, about 160 km downriver, you must bring your camping gear, guided trips are expensive, but if you have experience and are in good shape, this could be the adventure of a lifetime.
If you like fishing, go give it a try to capture a giant Tarpon, weighing an average of 140 plus pounds, for this you must rent a boat, or pang. There is even a national fishing tournament in San Carlos every year.
As most of this region is close to lake Cocibolca and numerous rivers, fresh, high-quality fish can be had for roughly the same prices as comparable meat dishes almost everywhere.
A particular specialty in this area are the so-called giant river shrimp, or "camarones del rio". These resemble large crayfish or small lobsters, and are quite delicious. Typically you'll pay thirteen dollars for a plate of three. However they are not around year round, as it is illegal to catch them from February to April.
As this area is not as developed as the Pacific side of the country, caution regarding tap water is recommended. In most places, running water is only available during certain hours of the day. However, all but the most basic hotels should have a tank that enables you to shower at any time. Bottled drinks are generally safe, but if you are suspicious, look at the cap before opening, because sometimes people just fill empty bottles with tap water. Ice is often made out of tap water; whenever in doubt, ask whether something is made from agua purificada (purified water) or not. Remember to stay well-hydrated, as temperatures and humidity can be especially challenging in this part of the country.
Although this isn't really a party destination there are some places for your Toña or Flor de Caña. For more see the individual city articles
Since the construction of the new carretera from San Carlos to Managua crime has risen somewhat, still the area is not less safe than most of Nicaragua and probably safer than the big cities. The normal caution should apply and taking taxis at night in San Carlos when going home from the bars and discotheques is certainly advisable.
In the Rio San Juan (as well as in lake Cocibolca) there are some bull sharks (yes seriously!) that are known to have attacked humans. As their numbers are very low humans are probably a bigger danger to them than the other way around, but the possibility of an attack exists.
When hiking through remote areas guides are always a good idea as getting lost is less fun than having somebody who can explain plants and wildlife to you.
Malaria and especially Dengue are more likely along the Rio San Juan than in more urbanized parts of the country. Dengue is transmitted by a type of mosquito that is only active during the day whereas the Malaria-mosquito is active during dusk and dawn but also at night. Doctors usually do not advise to take any medication against Malaria before the occurrence of symptoms and the Nicaraguan strain is comparatively harmless but precautions against mosquitoes (clothing that covers as much skin as possible, DEET-containing repellents (widely available, called "repelente" in Spanish) and mosquito nets (mosquitero in Spanish)) are certainly a good idea.
To combat mosquitoes local and federal authorities sometimes fumigate streets and houses. While it certainly looks frightening to those not accustomed to it, its health risks are much lower than those of the mosquitoes it helps keep in check.