The shallow, round pool was ringed with children and adults, their sleeves rolled up, their hands plunged into the water. A young woman with a microphone issued instructions. Suddenly a youngster screamed with surprise and pleasure as one of the dozen or so rays circling beneath the surface of the water brushed his outstretched fingers.

The Mystic Aquarium and Institute for Exploration in Mystic Connecticut, is filled with treats like this for both youngsters and adults.  The indoor-outdoor campus, best explored in summer, aims to excite, intrigue and instruct on multiple levels. For adults, there is information about the complex ecosystem that is the ocean; for kids, there are caves to crawl into, critters to touch, numerous interactive games to play and plenty of short videos to watch. With remote controls, youngsters can even steer powerboats around one of the ponds.

The aquarium proper included the usual indoor exhibits. A giant octopus lazed on a bed of rocks, occasionally moving his huge head to observe the observers. An electric eel undulated arrogantly through rocky arches. Jellyfish, eerily white, floated, seemingly suspended in time. Piranhas eyed visitors knowingly.

Especially interesting to me as a scuba diver (see, for example, ) were the colorful tropical fish (including the “Nemo”-like clownfish), many of them much bigger than they ever live to be in the Caribbean seas where I dive. I also enjoyed examining the healthy coral, gleaming and pulsing as I have never seen it when diving.

But outdoors, things got even better. Sea lions scratched themselves and barked (there was a sea lion show as well, but I didn’t see it). Penguins roamed a spacious pen, the depths of whose pool are visible through glass on a lower level. Informative placards educated the visitor on habitat and behavior, including the fact that none of the 18 known species of penguins live in the Arctic – they’re all from south of the equator, with the ones on exhibit hailing from Africa.

For me, the unexpected kings of the day were New England’s only beluga whales, who swim beneath your feet when you stand on a bridge, arching and blowing so close you can see into their blowholes. And their underwater antics are visible just downstairs, where, like the penguins, the visitor can watch the giant white creatures speeding through their watery world.

Four times a day, a team of employees appeared with buckets of fish for whale feeding time. This combined with a training session, in part to prepare the animals for human attention, should they become ill. This event always drew a crowd, as the docile giants smilingly gulped down whole the small fishes tossed into their gullets.

Side exhibits detailed underwater rescues of PT109, which was piloted by John F. Kennedy during World War II when it was rammed and sunk in the ocean off Australia (for more information and photos ), and of the Titanic, which had sunk in water 2 miles deep. There was even a motion ride theater (which I didn’t try).

A number of placards emphasized the fragility of this beautiful system, and the importance of preserving it by not eating overfished species, by helping clean up polluted areas, by practicing organic gardening techniques and by electing pro-environment politicians (for more information). Roaming guides were always at the ready to give information and help visitors understand what they were seeing. There was even an area (off-limits to tourists) where stranded seals and other wildlife were nursed back to health, to be returned to the seas.

Entrance to the aquarium was pricey: a family of four cost $60. But you can spend a pleasant weekend there — by getting your ticket validated, you can come back the next day at no cost. And you can throw in a side trip to the fascinating and tastefully rustic Mohegan Sun casino a short drive away, where there are unusual Native American exhibits and history, free entertainment and plenty of casual dining.

Accommodations in Mystic and neighboring Groton are plentiful but somewhat misleadingly advertised: When I called the Best Western for a published rate of $39 a night, I was told that this applied only to walk-ins based on availability; if I wanted to make a reservation, I had to pay over $100. And even on a showery mid-May weekend, reservations proved necessary.

I ended up staying at the Groton Inn and Suites http:// www.grotoninn.com, again, with a little difficulty. I was told that a room cost $159 (not the $68 advertised price), but for $20 more I could upgrade to a suite (which I chose to do). And indeed, the bill I signed at check-in totaled $179. However, when I found myself squeezed into a small, somewhat smelly room, and called to ask, I was told that the price of a single room added up to $179 with all the Connecticut taxes. However, eventually the staff agreed to upgrade me to a pleasant, spacious suite at no further expense.

Dining in Mystic also was something of a mixed bag. Dinner at the Seamen’s Inne, touted on the literature as a landmark, was unremarkable, both for the food and the atmosphere (except for the clam chowder, which was heavenly), and the advertised view of the ocean did not apply if you ate inside. However, a meal at S&P Oyster Co., where you could look right out onto the Mystic River, was delicious, although the featured shellfish in the Lobster Alfredo had to be extracted from shells smeared with gooey sauce. Diners chose from four kinds of oyster preparations — the one called Our Own Way was delicious.

And both restaurants appeared as kid-friendly as the Aquarium, with sturdy wooden tables at Seaman’s Inne, and crayons and paper tablecloths at S&P. The waitstaff was as friendly and welcoming as at the museum. (Next issue:: The amazing Mystic Seaport Museum of America and the Sea.)

Happy traveling!

Captions: 1. These harmless rays were available for petting in one of the Aquarium’s indoor pools. 2. Surprisingly beautiful jellyfish floated in one exhibit. 3. The aquarium labeled this a clownfish; specialists say the actual “Nemo” model was the false clownfish or anemone fish.

4. A gentle beluga whale seemed to smile in anticipation of dinner. 5. Mashup, a giant in Mohegan lore, lights his pipe with lightning in one of the murals at the Mohegan casino.