By the late 1960s, Japan’s early postwar avant-garde had largely petered out. The radicals of yesteryear were now 20 years older and the country had returned to material affluence and international acceptance symbolized by the 1964 Tokyo Olympics.

Following the anti-art movements from the early ’60s, conventional arts such as painting and sculpture became passe and action/happening/event-type performances acquired prominence. Enter the amorphous troupe The Play, active in western Japan, whose archival documentation now on show at the National Museum of Art, Osaka, celebrates 49 years of ongoing activities.

“The First Play Exhibition” (1967) took place in a park in Kobe at dusk and concerned a series of happenings performed by individual members. Later calling them actions and projects, they shifted to large-scale group-focused collaborations. Rather than making things for museums, they went outdoors and devoted themselves to experiences that emphasized everyday activities, including eating, sleeping and physical movement, though it is difficult to see how any of these had realistically been demoted or de-emphasized elsewhere in society.

The Play hatched plans at picnics, made preparations, undertook actions and compiled reports. With a fluid membership including more than 100 participants who banded and disbanded over the decades (only some considered themselves artists), active members now number five: Ikemizu Keiichi (b. 1937), who participated since the beginning; Kobayashi Shinichi (b. 1954); Suzuki Yoshinobu (b. 1948); Nii Seiji (b. 1946); and Miki Tetsuo (b. 1944), who was on hand as an assistant when the group started.

Failure and goofiness were frequent. For “Voyage: Happening in an Egg” (1968) the group made a big white egg out of plastic resin and set it afloat on the Kuroshio current off the coast of southern Wakayama. An expectation was that the egg might go as far as the American West Coast, but it disappeared. “Eggs in Orange” (1969) involved eating hard-boiled eggs, drinking Guinness and tug-of-war and aerobics. In “Sheep” (1970), members were to herd a flock on foot from Kyoto to Kobe, but after eight days they quit halfway to Osaka.

A more, or less, spectacular failure was the 10-year project “Thunder,” which began in 1977. Assembling and then dismantling a pyramid with 20-meter high sides made out of 500 leased logs every summer on a rented hilltop site in Kyoto, participants took out accident insurance and awaited lightning to strike the structure. None did for the first three years, so they decided to end the project once lightning did actually strike. It never did, though, and the summer excursions ended in 1986. “Yellow Pipe” (1988) was a less physically intensive successor project. Group members took yellow-painted cardboard tubes to an abandoned mine on Mount Oe in Kyoto and took pictures posing with tubes against the excavated backdrop, or of themselves camping. Other similarly odd performances were canceled or never realized.

Repetition has also been frequent. In “Current of Contemporary Art” (1969), members piloted a Styrofoam raft in the shape of an arrow from Kyoto to Osaka down the Yodo and Ookawa rivers. They did a similar thing in 1972 with a small-scale tatami floored plywood house that members lived in as they sailed down the Kizu and Yodo rivers. The house was burned when they could float no further. “Nakanoshima — Current of Contemporary Art” (2011) again involved piloting an arrow-shaped raft through Osaka’s waterways, and when the same was done in France in 2012, it was called “La Seine.” In 2015, they made another floatable house and cruised it down Osaka’s Dojima River. Such performances became a kind of B-movie zombie that would not die and just kept coming back in less compelling sequels.

The Play has mostly been fun and games for those involved. Since the 1990s its activities waned with nothing much happening in the 2000s. Reviving the momentum in the last few years through the repetition of the past, however, has been consciousness-raising and now museums and scholars are attempting to take The Play more seriously. But it is simply awkward or hyperbole to call their performances “migrations”? Or eccentric to describe floating down rivers on houseboats “temporary forays into communal living,” and goofy get-togethers as “unprecedented interventions”? With the exhibition composed of only notes, photos and snippets of audio and video stuck up on plywood held vertical by scaffolding, there is also not that much to see.

The offbeat late ’60s and early ’70s was The Play’s time. Now calling the group avant-garde going on 49 years is an oxymoron. From the later ’70s protracted decline ensued, along with the onset of creative exhaustion in the absence of new ideas. But that would not have bothered the spirit of The Play’s early years. All was undertaken with humorous sincerity within a basic framework of performing a planned action at a given time and place without a specific purpose or prevailing ideology. The Play imagined no definitive reasons or logic underlying their actions, and so obtaining practical results, they seemed to think, would be narrow-minded.

“The Play since 1967: Beyond Unknown Currents” at The National Museum of Art, Osaka, runs until Jan. 15; 10 a.m.-5 p.m. (Fri and Sat until 8 p.m.). ¥430. Closed Mon., Dec. 28-Jan. 4 and Jan. 9. www.nmao.go.jp/en/exhibition/2016/ play.html